Sorry, very late to this conversation.
Suggestion: Give them something. Run a once a month class for the basics, how to fix a flat, adjust and inspect brakes, maintain chain, inspect gear train, adjust derailleurs. I taught this, fast I admit, in 3 hrs. for a decade. Expectation was they could return during Open Shop and get more hands on asssistance with a basic understanding of what they were doing.
When I simply showed up on my own and asked if any new volunteers would like a couple of quick lessons, I never failed to get volunteers enthused that with these basics, they could start to help and get practice. They were already sick of simply tearing bikes down with no idea why or what the parts they were removing actually did. Ask, not demand, some time back, 6 hrs? Many will, those that don't oh well, was a cheap investment.
What truly amazed me over my decade of teaching basic maintenance, well over 200 classes, is how often this suggestion is rejected out of hand. A three hour investment is too much? Really? Worst case you have given another volunteer a chance to help out in the class to reenforce what they learned. The syllabus I used is on the Bike Wiki. The basics they can use immediately, not the "Build a Bike" where they do a hub but can't fix a flat. Air, Brakes, Cables/Chains/Dérailleurs. Also a great way to help someone if you do open shop assess their bike when they think they only need a derailleur adjustment while in reality the V brake adjustment is so far off it's an accident waiting to happen.
Just my $.02. But what's the classic definition of insanity? Doing the same thing over and over and expecting a different result.
Ron