That is true and the reason for that is not capitalism, of course. Most projects don’t have UI experts and when someone wants to help, devs usually don’t listen. Sometimes there are technical obstacles too (old framework, hardcoded UI), but probably not in web or Electron apps.
compared to their paid alternative
Keep in mind that Libre Software can be commercial too, so you really mean proprietary alternatives.
I know, I just wanted to explain the real reason why their UIs often suck. I agree that it has nothing to do with capitalism.
Lemmy is a perfect example of such project, btw. The devs can’t design a good UI themselves and they ignore people’s proposals, so users make their own themes and browser addons to fix it.
We can have nice software, people just need to care.