[ducktective]

There is libgtk, aside from breaking changes between versions, some projects just don't want to "put up" with arbitrary decisions of upstream. Hence QT and KDE for example. But that has LGPL issue.

Until a major backer steps up and funds a project with amounts that is comparable to what MS or Apple spends on their GUI, the Linux on desktop is not happening.

My bet is on QT if anyone is listening.