As something of a dumdum myself I think I know why. Corporations want people to be able to do their thing as easy as possible to make money, while people not directly motivated like that and not motivated to make it as easy as possible can do anything else. So instead of "make sure it's just a button click" it's "what, you didn't read all 580 pages of the documentation and all the changelogs and the code on github and compile it yourself on a custom built $40,000 machine? We don't help your kind around here go away" and yeah people go right back to windows or twitter or whatever.

Jokin aside I'm just trying to explain there is a real problem there. Feeling smug about the result of that problem doesn't fix it but it is really easy to do

The difference between self-hosting most things, and Twitter and Reddit (and Facebook and Slack and Discord) is the network effect. If I wanted to self-host my pictures that I share with friends, I can still just send them the URL. They might be annoyed that they're not on Instagram and have to use a web browser instead, but the people that want to see how my long weekend went will go see the pictures. To self-host something like Reddit, I need to convince other people to change their habits and their choice of platform. As not-a-million-dollar-corporation, my ability to have a polished UX is rather more limited, so I can see why someone would go back Twitter and Reddit.