Just like using a Mac after having been a PC user; or being forced back to MS Windows after using Linux/KDE for a couple of decades.
I used to use Inkscape heavily, but having not used it for a few years, I go back and the UI has changed, similar experience; I feel lost when I should feel capable.
Photoshop was one of the first applications that I noticed using the 'give it free to college students to capture the market' technique. That works so well because it takes a couple of years for for you to adopt the software as an extension of your way of thinking - changing application means a productivity loss, and a feeling of incompetence, and no professional wants that unless they can clearly see an ultimate gain.
I mentioned it in a different post, blender is the prime exhibit for this, its UI received even more criticism than gimps. Now that it has become the (or one of the) most popular 3d modelling tool, most of these voices disappeared, because it has become the first entry point and people are not used to some other way of working anymore.
If anything Blender proves that paying close attention to UI and making it mostly align with user expectations matters.
And my point is, regardless of those claiming gimp sucks because it’s not what they’re used to: it absolutely does not matter an iota because there is near universal acceptance that it’s terrible for anything but toy work. UI aside, internally it isn’t fantastic either, a problem that blender didn’t have.
It's like people who speak English talking about how everything in Spanish is in the wrong place. It's the cheapest way to bikeshed: make it more like the thing I know already!