@evanEvan Prodromou
@tedTed Gould If you think someone is obligated to put work into something despite not being paid, that's called entitlement. If you want to ensure they keep working on something, you should make it worth their while. Otherwise you're just exploiting them and demanding free labor. It's the same thing as "working for exposure".
What their goals are is entirely orthogonal to the question you asked. Your question was broadly applicable. Narrowing the scope is moving the goalposts.
And I say this as someone who's put tens of thousands of hours into FOSS projects without the promise of compensation.