What is this mutually shared meme-delusion that Gimp is anywhere close to an adequate facsimile of Photoshop?
It’s not a facsimile of Photoshop but it serves the same purpose.
In my experience the people who come to GIMP expecting it to work exactly like Photoshop are the ones who are disappointed, because it’s not Photoshop. But if you use it and don’t expect to already know how to use it because you know Photoshop, it’s fine.
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.
Does it take less cognitive cost because it’s actually easier, or because you’re used to it and you’re not used to GIMP?
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).
The hyperbolic invective hurled at GIMP by Photoshop users is astounding. I often spend all day in Photoshop and Illustrator doing preprint and it makes me want to burn Adobe to the ground every day. I would gladly never look at PS again if GIMP got color right.
For some it apparently is. There are certainly talented designers/artists who really want an open source stack who can produce excellent results using GIMP. Would I encourage using GIMP if someone doesn't care about open source? Almost certainly not, but it can be used to produce excellent results.