You make an excellent point, and I've never thought about it this way before.
Devs are not newbie friendly at all. We were all noobs at some point and (if we're being honest) remember the excruciating pain it took to become versed. Most people are not going to go through this, so FOSS naturally loses a lot of non-tech talent (including UX).
What I didn't think about is that there really isn't a way for UX people to contribute at all. GitHub Issues, at most, allows for people to make feature-requests - but beyond that it's just not viable.
For example, I am a UX designer and would like to contribute or iterate a layout. My demonstration includes several images and a video. First off, where do I do this? I could use GitHub Issues, but this is an extremely painful process that is likely far removed from my normal workflow. I could use YouTube, and then link on GitHub issues - but then I have to jump through several annoying hoops for a still sub-optimal workflow.
Git itself also has worked very poorly with binary files (png jpg mp3 wav...) until the recent advent of git-lfs. Binary iteration using base git is just a non-starter.
I am shocked to say it, but I cannot think of any development UI that is actually decent for non-tech people. If anyone does FOSS UX, and I am wrong about the tooling, please correct me.
This is true, but only for now.
The point of decentralized social platforms is to eventually include everyone. This is not to say this is Lemmy's goal, but it is certainly the goal of its users. The tech-illiterate will show up en-masse (they always do) and what will be our answer for it? From what I see, we have none - this is no different than living on borrowed time.
We have to remember that "enshittification", before all else, is a cultural issue. When the people that have this culture arrive, the whole platform will suffer for it (hence what I said earlier). Humans are just better with dealing with this in real-life, but the internet poses a lot more challenges that I just do not think we are ready for.