I mean, there's something to be said about adhering to an industry standard. Of course no project has to do so if they don't want to, but people trying to get on with their work don't want to spend a bunch of time relearning everything. I think Blender really thrived when they loosened up a little on their ideas of what a workflow should be and gave people industry standard options out of the gate.
Whether we like it or not, GIMP isn't going to be most people's first experience with image manipulation. Whether they had a free PS license through school/work, had a subscription at some point, or once got it through ahem alternative means, people will be coming into GIMP with certain expectation of what the workflow should look like and will get frustrated pretty quickly.
this doesn't even bring in the question of IP and rights to software itself. If GIMP implements an option perfect workflow of photoshop, does that mean adobe can just sue GIMP now? Because they're basically the same software.
Blender's UI has seen incredible changes in the past several years. To the point it has become exceptional today. For a program that accomplishes so much (3d modeling, rendering, compositing, video editing) it manages to keep everything very intuitive and easy to use. Gimp --a fucking image editor-- is like trying to solve quantum entanglement theory.
There was a very distinct switch between ~2.7 to ~3.0 where they actually started listening to the users. If you look up the release posts on social media, you can see the community talking about it at that time. Many of them touch on the exact issue of GIMP failing where Blender succeeded.