Arguably, Clementine is a counterexample to your argument.

Many years ago, the Amarok music player was very popular on Linux; I used it extensively, as did many people I know, even though none of us used KDE (the desktop environment on which it was built).

Then, the Amarok developers decided to revamp the project for version 2; using newer technologies, removing bit-rotten code (apparently, due to the large userbase, there were many "drive-by patches" from one-time contributors, who were never heard from again) and, most significantly, completely rethinking the UI.

If you dig around a little, you can find a lot of documents following this process, e.g. from the (now defunct) Amarok blog https://amarok.kde.org/blog

The result? The snazzy, powerful new music player known as Amarok 2 https://amarok.kde.org

Yet, a huge number (most?) users abandoned it, the Amarok 1 codebase was forked and renamed to Clementine, and years later this "horrible" music player is still going strong; so much that it appears on the front page of Hacker News.

Personally, I tried Amarok 2 for a while, but never really liked it. These days I use cmus ( https://cmus.github.io ) but my non-technical partner prefers Clementine. The only problem we've had with it is trying to use a RaspberryPi as a file server; building the player's database over a networked filesystem is painfully slow. It would be nice if there were some way to create the DB on the RaspberryPi and send it over to the machine running Clementine; but I've since been looking into Beets and MPD.

UX designers are scary IMO. Often they have totally different ideas about a good desktop environment than the rest of us. Might end up annoying lots of your users (Firefox) or even breaking it for a significant chunk of your userbase like Ubuntu did when they decided to imitate a certain fruit company. (Yep, between moving window controls, messing with the menus, breaking alt-tab just the same way as said company and even adding a dock, thats what they did.) Certain users like it, others like me left.

Edit: the thing it seems they don't understand is:

Firefox: the people who prefer Chrome already use Chrome or Chromium. We use FF because for some reason or another we don't like Chrome. (For me, that is extensions.)

Ubuntu: lots of us used Ubuntu because we really liked it, not because we couldn't afford anything else.

Do you know any UX designers who want to volunteer for such a thing? I'll bet you a shiny nickel that the Clementine people would be happy to accept contributions in the form of graphics and patches.

But because they are an all volunteer project, they probably can't accept sketches, wireframes, and color swatches as useful contributions, because you then need to organize people to implement these things.

The gap between "do this, it will work better" and "here's my pull requests" is large.

Try lollypop for a modern player with a very good UI. It's still in early development, and pretty fluid, but I'm using it as my day-to-day.

I particularly enjoy its focus on albums as elemental units of playback, as opposed to songs.

https://gnumdk.github.io/lollypop-web/

So you're saying that UX designers apply to OSS projects, but just don't get "embraced" enough?

But as others have pointed out, music players are a highly subjective territory. I for one liked iTunes a lot better before Apple unleashed designers on it and made this new color-adaptive, web-like mess out of it. I like data tables.

Clementine comes from an place where software is aimed at all levels of user - without sacrificing expert features. If your idea of UI and UX (I don't know) is the modern trend of hiding features to make software into toys then that won't go well with its users.