So, why do UI people not use and contribute to FOSS then? Are they all on Mac? Then go complain to them or contribute your desired UI improvements. FOSS isn’t an all you can eat buffet.
Personally, I think UI people are less idealistic and I do look down on them for that.
It’s super hard to get involved as a UI person. If you’re a developer, you can just rock up to a project and fix bugs, and if you follow the coding style they’ll probably get accepted.
If you want to successfully contribute as a UI person you have to convince a bunch of developers that you know what they should be doing better than they do. It basically never happens.