I've got a suggestion... but I'll be nice and offer this instead:
At your next meeting, have sign-up sheets for decorators, food police, drink waiters, invitations, clock watchers/timers, etc. Have a sign up sheet for everything, for every event you have planned in the future. Pass it around. Twice. Don't leave anything out, no matter how trivial. Two things should happen: they will realize what it took to put the party together without help and they will sign up or shut up.
I am the PTO Pres. at my daughters school. I feel I can never do anything right. Parents, teachers, etc... always have something negative to say. The latest was that the Christmas Party/Meeting was very disappointing, It did not last long enough, etc... We provided food, and drinks for all staff and members. It did cost a good amount of money. People were also upset that we did not decorate enough, some peope did not receive their invitation. It is never ending! My board and I are doing everything we can do to make everything run smoothly, but it just does not work. Any suggestions?