Some people have hobby projects they really don't want anything other than donations for. Sometimes they don't even want donations.

Money brings responsibility, and responsibility kills the fun. Donations will begin to feel like you owe the donators your time, even though you do not. But it's hard to break out of that mindset. Especially once you start getting negative remarks for not implementing enough features, despite the donations.

This feels like a non sequitur. Their project being open source or not doesn't protect their mental health spiralling. This could have happened to a paid lib, and you'd be out of luck due to vendor lock rather than just picking a fork.