Comment by BadBadJellyBean

We have to keep in mind though that many open source projects started as something that someone wanted and then made. It probably worked just like that person wanted and then it grew. Maybe it is because they weren't too versed in UI/UX design.

Another thing is that many classic open source projects don't have a "I want to grow my user base" mindset. Why would they. It's not like they get paid.

Big overhauls also always have the risk of alienating current users. I learned Blender on the pre 2.8 UI and because I use it rarely I still sometimes struggle with the new shortcuts.

Blender clearly benefited from the change but the real spirit of open source is: you don't like it then help fix it.