They did. Though you may be too young to remember. 👨‍🦳 Unfortunately the problem is unless they completely ape a more popular product. Many will still be unhappy. People still complain about blender as well.

That isn't to say the UI still couldn't use more Polish and decluttering. But with what money and who's time? I think that's the bigger issue. I know there are soft forks that imitate adobe. They could pull that into the main branch perhaps unless there's a licensing conflict. But who's to say adobe is right, not just familiar.

Honestly I think GIMP being it's own thing is fine. But here's the thing. UI/UX is much easier to participate in open source as a non coder. Look at the toolkit they are using. GTK 3 IIRC, and try to do a design based off that. There may even be a GUI builder like with QT. Where you could even define the GUI in a GUI, to make code for them. Or perhaps something basic like tool icon redesign.

Point is. While a lot of coders like to code in their free time. Or at least on tools they use. UX/UI or graphic designers are actually scarce comparatively in the space.