Every time image editing comes up on forums, so does mentions of GIMP. To me, there seems to be no shortage of "GIMP has UX problems" claims.
So what gives? Do they not believe that this is a legitimate problem hurting their adoption? Or do they not care about adoptions? Somehow it's not a priority? Or their execution is severely lacking.
I'm not in any way affiliated with GIMP or even a graphics professional but as a programmer I think part of it is ideological (GIMP is not a copy of photoshop, why would we spend a lot of resources to change something that works for us and copy adobe for example just to appeal to users who don't want to learn to use a new UI or workflow) and part of may be just because they are more or less happy with it, they have a steady user base (at least it seems that way guessing by the mentioning of GIMP on forums as you say), also it's not like they (programmers/community) are going to get rich off of it so there might be no profit motive in revamping the whole thing.
I think the project just needs some fresh blood, either a fork that strives for a (better) more familiar UX for people that are switching from commercial products or an easy way to decouple the UI from the core and build custom front ends. There's no point in re-developing all the functionality that's already in GIMP, it's a functional product with years of development behind it.
So what gives? Do they not believe that this is a legitimate problem hurting their adoption? Or do they not care about adoptions? Somehow it's not a priority? Or their execution is severely lacking.