People also just get wildly entitled.
I stay anonymous, but I built some software that people use for scientific analysis. I give it away; I don't put it on my resume; the only thing I've gotten from it is it makes me a bit happy that maybe I've saved someone else hundreds of hours of work. There's also some subtle numerical properties that take real work to get right.
(Not all, but some) people demand support, features, or bugfixes; and on their schedule. Or docs, or a prettier site, or blah blah blah, and every second of this takes away time from my real job, my now elderly dog, hobbies, etc. Recently there was a wave of it from some library weirdness on m-chip macs, which I don't even own. And they're guaranteed to get very pissy when I tell them I don't care at all (and, in several cases, if they want me to care they can start by shipping me a new mac and I'll think about it). I honestly mostly just delete the emails anymore because reading them makes me wonder why I'm wasting time on a computer.
As I mentioned, sharing makes me happy and feel like I gave a bit back, but all the shit that comes after that is ugh.