It's hard to fault anyone in that triad 100%. Open source has a way of becoming infrastructure. People come to depend on tools made by people without the resources, interest, or personality to run an infrastructure project, or who won't budge on their vision to allow contributions outside of it that might help get the project to a point where it can attract enough vision-aligned contributors.
Forking potentially shifts the problem to a new triad, so it's not an obvious solution in all cases.
I've come to call this "fenceware": technically open source due to its licensing, but community-wise it is as if the developers just throw a ball of code over the fence every few months. Sure, they let you play with it for a bit, but it is not yours to co-own.
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.