I think, for the most part, is that GIMP is obscure. Not as in ‘unknown’ but as in ‘really hard to master, how does anything work?’ It has been this way, voluntarily.
I think it’s what lacks in GIMP, a good user experience.
I have used gimp for the better part of the last ten years. It’s good. I have used Photoshop less than ten times in the same timespan. But when I need to do something, it will always be easier to me on photoshop, eveh though I’m not acquainted with it…
Edit : May this post serve as a remembrance not to suggest an easy mode on FromSoftware game 😁