Moderation is thankless work that comes with heaping helpings of scorn from the community. Even if you're doing it purely because you want to see the community succeed, you will be accused of doing it because you're a petty tyrant who likes to lord it over other people. Plus, of course, moderation itself is work and it's usually not very fun work. I've moderated online discussions before and it really wears you down after a while.

It doesn't surprise me that it's hard to find a lot of trusted users who also want to be moderators.