I have a vague recollection that twenty years ago GIMP paid some designers to come up with a great UI, but once the design was ready, GIMP was like "nah we don't like that" and kept their bad UI.
I do image stuff so rarely that GIMP is fine because it's free. But its UI is so bad. I don't know about now, but I remember a few years ago someone pointed out that GIMP had over a million dollars in a Bitcoin wallet and hadn't touched any of it in like a decade.
Gimp still has a lot of good features that I find myself crawling back for, on bigger projects. But Pinta has that good ol' fashioned Paint.NET feel to it that a lot of people still strive for.