Because the tea party has no credibility. And the tea party can't see that.
Tea party ragers like Glenn Beck have attacked Obama for everything under the sun since before he was even elected.
The tea party scree is a collection bitter partisans, bigots, bullies, anti-government paranoids and sore losers. Nothing they have done has given anyone reason to think anything else of them. And Glenn Beck's admonition to stop wearing tri-corn hats in public really didn't help.
Only their insane base is fired up by their every-day-is-Armaggedon-in-America fevered hysteria, that has gone on for long years now. We have reached the point of complete over-saturation and burn out.
They pounce on Obama's every mundane activity or inconsequential gaffe as the epic fail of a lifetime. How dare he play golf during a time of war! How dare he, the President of the United States, see a play in New York City with the First Lady! He used a teleprompter! He, the father of two young girls, told school children to study! His dog adoption was illegal! He vacationed on Martha's Vineyard! He bowed too low! He smoked a cigarette! He put spicy mustard on his hamburger! Michelle Obama touched the Queen's back! Wahh! Wahh! Wahh!
Their goal is foment fear and hatred, stir up trouble and fling mud, desperately hoping for something - anything - to stick. Neither integrity nor fairness plays a role here. Any smear job, no matter how foul, dishonest or racist, will do. The more absurd the better, in fact. Kenyan. Secret Muslim. Socialist. Communist. Marxist. Chupacabra.
Do they even hear what they sound like? Does it get any more stupid or petty?
Perhaps if they hadn't behaved like loud-mouthed violent bullies and liars from the start, and well before the 2008 election, someone may take them seriously if they had a valid or reasonable point about anything.
However, they have cried wolf so many times that most people just shake their heads and dismiss them as whiners and unhinged nuts.
They are confounded by the fact that no one with real integrity will listen to them because they lack even the tiniest amount of self awareness. They are incapable of seeing themselves as others see them.
This is why the Benghazi smear is circling the drain just like every other false bleated accusation from the tea party crazies. Smears, bullying, threats, witch hunts, bigotry, idiocy and non-stop whining is not how a political organization builds credibility.