public amenities are regularly given to cities by benefactors who live in the community
That only makes sense, when the subject is tangible property. Does anyone even own the software projects in subject?
What you said is a pithy false dichotomy that disregards any and all motivations other than pay and pleasure.
No. You pick that litter because it gives you pleasure — you've improved the world around you, and can feel better about yourself. You're under no obligation to do it. I know, that this is, what motivates me to fill out bug-reports, donate my own code, return shopping carts, and, yes, pick up litter.
disagree with your thinking that such demands are being made here
Well, I'll be happy if you end up being right.
Could you specify what you took as a demand?
The implication, immediately following from the (rhetorical) question, whether the current model is "sustainable", that the current state of affairs is, in fact, "not sustainable". Which further implies, the development may cease if someone does not pony up the donations.