Blender is unique in having a big set of users who are actually good at aesthetics professionally. A subset of that group wanted to contribute, and the technically minded were actually willing to let them.

Most other open source projects have people behind them who don't put UX first, and who are suspicious, jealous, or plain disagree when people want to help with UX.

This shouldn't be too surprising in a world led by people who value technical excellence most.