I pop into a lot of different regular diaries that use rotating diarist duties, including WYFP, WAYWO, DK Quilt Guild, Books that Changed My Life, as well as others. Some of these regularly call for new hosts to help with upcoming posts.
People hesitate to volunteer for these, just as they hesitate to volunteer for other activities. We all do that, I think, partly hopeful that someone else will take care of things, partly out of insecurity about being able to do a good job, and partly because we don't know what will happen with our own lives in the intervening time, if we can even show up as we've said.
Sure, it would be great if there was always "someone else" who would take care of community activities, if our own help was never needed. But sometimes you need to step up and be the one. If not you, who?
And a lot of us feel insecure about being able to do a good job, especially if we've never hosted that one before. For example, I volunteered to host an upcoming WYFP. If you've ever been in that diary, you know the author's post often is a heartfelt story of a serious problem in their own life, caretaking concerns, illness, death... I don't have those issues in my life, so how can I "compete" with them? No need to. My FP may be small or somewhat trivial as compared to those, but it really doesn't matter either way. The most important part of hosting a diary like that is to be there.
"Being there" includes keeping your commitment. There are multiple times I've seen that someone volunteered to host a diary for a weekly spot, and simply didn't show. For at least one of these, there was no notice from the expected diarist. That's like calling a meeting and then not showing up to run it. Not acceptable under any ordinary circumstances.
If you DO commit to hosting, then make sure you've provided a diary, checked on what tags and banners are expected, how and when the diary is to be queued, and how to do that to make sure it shows up where it is supposed to.
As to "hosting," I think for ALL diaries, the diarist has a responsibility to be there. That means posting is not the end of their duties, but the beginning. Some people compare diary posting to hosting a party. If you are a guest, you should be polite to the host and not start a fight in their house. If you are the host, you need to make sure the guests are comfortable. To me that means the diarist should read and respond on an ongoing basis and should acknowledge comments even if in disagreement. The diarist should NOT post and run. If running is required, it's polite to include a notice, such as "I'll be out for a few hours but will respond when I get back."
Don't be afraid to take on these duties. It can be a lot of fun. For new diarists, it's a great way to get their feet wet in an established forum. And it helps ongoing series continue. Without community involvement and help (not just reading and commenting), some of these series would die.
So step up, help out, take your turn and be an active and welcoming host. Your guests will be glad you did, and so will you.