Commercial products work on different timelines and have different goals, and ultimately the developers are often not the users so they don't really care one way or other to follow somebody else's design.
Ideally you get somebody who is both a great designer and a coder but those are few (Asesprite comes to mind)
UX designers want money, and free software projects are rarely a paying gig.
GIMP collaborated with a UX architect between 2005 and 2012. That guy was paying for this stuff to his employees out of his pocket when he was able to.
However I think that people are okay with doing stuff for free as long as it is fun. Being your own master is fun, but if you need to collaborate it will quickly become work.
For people moving in the other direction, it's photoshop that's not intuitive. I don't want a single-window interface.
I wouldn't mind an entry-level image manipulation system that starts by giving me only a few obvious functions, and lets me grow into more advanced functions as I learn more, but that's probably too much to expect.
On the other hand, serious image manipulation is no doubt a serious skill that requires training that I simply lack. Someone with no programming training failing to grasp Python or Java doesn't mean there's anything wrong with Python or Java.
I've grown more accustomed to GIMP since my job doesn't justify Adobe prices. But it's still quirky to me.