Precisely. "It's fine" is the problem. It doesn't need to be fine, it needs to compete with Photoshop to be a serious tool in the space it serves. And what the vast, vast majority of artists have said is that it is insufficient for that.
Can you crop a photo in it? Sure, once you figure out the placement of things.
Can you perform serious photo manipulation? Somewhat, although Photoshop takes way less cognitive cost (so more people can be more productive).
To be frank, I'm a regular GIMP user and have only dabbled in Photoshop. However, I empathize with daily drivers of the software.
To address you're question: elements of both.
As a paid service, Photoshop can afford to have developer research users and improve UX. GIMP, as an open source project, is subject to the (often well-placed) whims of its developers, which does not have the same profit motive to keep users as Photoshop.
This in of itself does not guarantee less cognitive load. But certainly it is easier for a GIMP user to adopt Photoshop than it does for a Photoshop user to adopt GIMP.
Further, we could argue the status quo is as it is because GIMP is less productive than Photoshop by at least whatever Photoshop charges per month (and possibly more).
Can you crop a photo in it? Sure, once you figure out the placement of things.
Can you perform serious photo manipulation? Somewhat, although Photoshop takes way less cognitive cost (so more people can be more productive).
Economics of attention are important.