I've seen it for years and years now, and I can only conclude that it's down to the kinds of people who are attracted by these kinds of projects.

They're tech literate at a professional level by necessity in order to engage with these things at an early time in their development, and this seems to drive a mentality that makes UX design kind of an afterthought, since they already know how to do the things they want the software to do, and they're not focused on how less tech literate users will handle it.

Then you add in the small minority of gatekeepers that wind up in every community, who feel that a larger, more generalized userbase would be invading their niche community, and you end up with stuff like the Linux forums where asking a simple question would get you a series of remarks that essentially boil down to "go fuck yourself, you should know how to do it already."

I feel like the people concerned with UI/UX come into these kinds of projects later on after they've matured a little, rather than right from start, and this causes resistance to their changes because the userbase is already entrenched in the current UX, especially from the gatekeeper folk in the community who see a higher tech literacy threshold as a good thing.