I've joined several and each one has fizzled out for one reason or another. Most people have had their reasons for leaving and that's fair. But given my experience here I don't feel like putting in a lot of work into someone else's idea anymore, because of the failure rate. I'd rather do my own project now, even if i have to learn how to program it.
At least if (or when) it fails it would be my own fault. :)