Many people who would benefit from having a service dog don't have one.
The ultimate reason is a simple one for which there is no quick remedy: there is a distinct lack of people and agencies who can provide trained service dogs.
There are also a lot of fraudulent trainers who provide horribly expensive and not well trained service dogs. I know of a young girl who was severely allergic to peanuts, and her parents acquired a trained peanut allergy dog for her, only to discover the dog not only didn't alert on the presence of peanuts, it had a fondness for eating peanuts and peanut butter. The agency refused to retrain the dog, provide a different trained dog, or refund the fees.
Disabled people get ripped off frequently, and getting ripped off in the case of a service dog is particularly hard. Pretty much the only training agencies that are guaranteed to provide a properly trained service dog are the guide and hearing dog agencies - and even those have a few "bad apples".
If you're disabled and need a service dog for anything but sight or hearing assistance, you have to really research the agency. Even then, there's no solid guarantee the dog will work out with and for you.
A few agencies provide a service dog at no charge to the disabled, but many charge, and charge a lot. It's not exactly an exact science to train a dog, and many dogs wash out. The cost of training the wash-outs still impacts the bottom line of the trainer or agency training the dogs, and that cost is passed along to the people who receive the dogs that do get trained. Thousands of dollars, in many cases.
And it's not just the cost of the dog itself. If it's a reputable agency, there's the acclimation training, and that can be a week or two with the disabled and the dog being trained together - hotel, meals, transportation, not to mention the cost of the equipment.
I know a lot of people call service dogs "tools", but "assistants" is a far better term because they are living beings and they do feel pain, get tired, get distracted, and when provoked enough, will defend themselves. To treat them like a wrench is a disservice to the dog and the handler.
Because they are not just "tools", service dogs require care. They need to be fed, toileted, vaccinated, given periods of rest and play, and receive proper health and dental care. This is not cheap, even with health insurance, because the best insurance still has breed-specific exclusions, and doesn't cover routine health care.
In addition to that, service dogs require equipment. Depending upon the service(s) the dog provides, the equipment ranges from a harness and leash to special harnesses, weather protective gear (booties, sweaters, coats, rain gear, eye protection, ear protection...), and specialized gear (pocketed vests to carry medications and supplies), and - for their protection - vests with warning labels on them (Service Dog - DO NOT PET). These cost more than a pet dog's collar and leash.
And after all of that non-refundable expense, the dog and person may not be a good emotional fit.
Reputable agencies will work with a person to get a good fit between dog and handler. Not all agencies are reputable.
All these expenses make it impractical for a poor person to acquire a service dog. Even though service dogs are called "tools", Medicare and Medicaid do not pay for service dogs for the disabled. The IRS does allow a disabled person to take a tax credit for a service dog, so the IRS is more humane than the agencies that persist in referring to service dogs as tools.
Fortunately, disabled people don't have to rely on agencies to provide them with a service dog. They are allowed to train their own service dogs.
Among the bonuses of training your own service dog, there are also pitfalls, just as there are pitfalls to receiving a dog from an agency.
If you use a dog you already have, you have a dog with whom you know you are compatible. That's not a guarantee with an agency-provided dog. It is really important to have a bond of trust with the dog who will be assisting you. That bond is not always present with an agency-trained dog. With time and effort, it could be acquired, but I know, for a fact, that I am not personally compatible with terrier breed dogs - and most excellent hearing dogs are terrier type dogs. It would take a very special terrier to work with me, above and beyond its training. I am also not very compatible with many larger dogs (Dogmatyx notwithstanding) and most agencies prefer to train large dogs as service dogs.
The downside to this is that the breed you use may not be recognized by the general public as a service dog, like Itzl.
You will have to pay for the CGC, you may have to pay a trainer to help you give the dog basic training and socialization skills. Those fees are negligible compared to the cost of a fully agency trained dog (excepting those few agencies that provide the dog free to the client, relying on donations and grants to fund them). This training and certification is crucial if you are training your own service dog. A reputably trained agency dog will receive this training; a self-trained dog also needs it.
Receiving a service dog from an agency has all kinds of barriers for disabled people who are lacking in the financial department. Being able to self-train a service dog means that people like me can have the benefits, support, and freedom a service dog provides. There's no way I could ever afford an agency trained hearing assistance dog, and even if I could, because I am not fully deaf, I would be placed at the bottom of any list for receiving a hearing assistance dog.
Itzl has saved me from serious physical injury several times in our 8 year partnership, and he's probably saved my life a couple of times because he alerted me to sounds I didn't hear that connoted immediate danger. Although we haven't had a tornado through my neighborhood, one did touch down less than a mile away. I can't hear the tornado sirens. Without Itzl's alert, had that tornado turned just a little bit, I would have been caught completely by surprise. I don't generally have the TV on unless I'm watching a closed captioned movie. If Itzl alerts me to a tornado siren, I can turn the TV on and watch the weather alerts (a weather alert radio is just not going to do me any good at all, therefore I don't have one of those among my survival gear). Itzl also alerted to the fact that someone was stealing my car, and helped me prevent that. I know, it's not a life saving thing, but it saved me thousands of dollars and allowed me to keep my job - which, in a round-about way, did save all our lives.
Self-training means you can train the dog to provide the specific tasks you need rather than standardized skills. There are a few service dogs that need to know standardized skills (guide dogs, allergy dogs) but most need skills tailored to their handler's needs and their handler's personality. Over time, an agency trained dog will adapt to the handler, but why waste time adjusting to one another when self-training automatically incorporates those specific needs and traits?
Depending on your disability, you will need outside help to train the dog, even if you were an experienced dog trainer before you were disabled. As a hearing impaired person, I need others to help me teach Itzl new alerts and new sounds. We've been partnered for 8 years now, so we're pretty settled in how we relate. Some people swear we're telepathic, the alert and response have become that seamless. But I still need help teaching him alerts to new sounds I can't hear. Sometimes, he realizes I can't hear the sound and signals to me "new sound". And sometimes, I need help reminding him to alert to sounds he lazily decides I don't need to know - like the noon sirens on Saturday, or tornado sirens that sound, stop, and then sound again - he used to not alert on the subsequent alarms.
With luck, there's someone around to identify the sound for me and I can then train Itzl to it. For those who are vision- or hearing-impaired, outside training help is important. For those who have mobility issues, particularly those who lack the strength to direct or control the dog, outside help is important. For people with allergies, they need someone who isn't allergic to train, up-train, and reinforce training.
People who have never trained a dog before need outside help in training one. The very least they need is basic puppy training (if their dog is a puppy, if not, basic dog training) and training for the CGC (Canine Good Citizen) certification. They need to be able to complete the dog training assignments and be dedicated to the training process. They also need to provide the dog with a great deal of socialization in many situations. Doggie play dates at the vets. Walks in the park. Attending parties at friends' houses. Attending outdoor fairs and festivals. Walking near traffic. Visiting stores where pets are welcome. Traveling in cars and on buses. That sort of thing.
Once the dog is past its adolescence, it can be trained for specific tasks. If the dog is going to be a mobility dog, a balance dog, or a guide dog, most of it's service specific training should wait until the dog is physically mature because the physical needs would stress forming bones and injure the dog.
Dogs for seizure alerts, blood sugar alerts, hearing alerts, allergy alerts, migraine alerts, narcolepsy alert and response, autism support, PTSD alerts, psychiatric alerts, and retrieval dogs may be trained at a younger age than balance dogs, guide dogs, and mobility dogs because they tasks don't rely on size, strength, and physical maturity.
It takes between 4 and 10 months to fully train a service dog. Guide dogs are generally fully trained in 4 - 6 months, with a 2 week acclimation period between dog and handler. A hearing alert dog can be trained in 2 - 6 months. A seizure dog can take a year to be trained because of the intermittent nature of seizures.
Some dogs are best trained by qualified agencies. Guide dogs, balance dogs, mobility dogs, retrieval dogs, and allergy dogs benefit from the professional, intense training an experienced agency can provide.
Allergy dogs? Yes, because the training process requires frequent exposure to the allergen, which would be detrimental to the person for whom the dog is intended.
Service dogs require occasional up-training, and re-training because they pick up bad habits. Some of those bad habits are caused by "well meaning" people who do their damnedest to force the dog to break training.
Itzl is prone to thinking he knows more than me, and I have to occasionally remind him that while he can hear more than me and is a very smart dog, I am smarter still and I am the one in charge and control.
Perhaps the strongest reason to get a service dog from an agency is the confidence it provides the handler. Part of the training process is training the person on their rights as a handler of a service dog, and teaching them through experience what they are allowed to do with their service dog.
That's one of the biggest downsides to self-training - the lack of confidence in your rights as a handler of a service dog. It's not helped by all the people who are willing to believe you aren't disabled and you don't need a service dog, especially if your disability is an invisible one. It takes a lot of courage to go out in public with your self-trained service dog, and you always feel, especially at first, that maybe you're a bit of a fraud because so many people tell you so - and not always politely.
And sometimes, even with the best effort, a self-trained dog isn't suitable to be a service dog. In an agency, such dogs often find a home as a pet dog. If the dog is self-trained, it's much harder to admit the dog isn't suitable, and almost impossible to rehome the dog. Sometimes, the dog can be the at-home service dog, offering a respite for a dog who can be trained properly. Of course, most agencies won't place a trained service dog in a home that has a dog, even if the dog is a trained service dog (a real hardship if more than one disabled person lives together and have different service dog needs).
Xoco was a partial failure as a service dog. She does the alerting excellently and has that part down even better than Itzl because she never forgets to alert, where Itzl sometimes gets a bit lazy. Her failure comes from her injuries as a puppy, injuries she was never able to overcome. Fortunately, in hr case, she acts as a relief and back-up for Itzl at home, so he can get some respite from always being on duty. But if Itzl had been an agency-provided dog, I would have had to re-home Xoco before getting him.
When everything goes right - 2 + 4 = 1. You and your service dog become an inseparable team.
And when it goes wrong, whether you receive an agency dog or self-train, 2 + 4 may never equal 1.
And that's the saddest thing of all.