All I can offer you is what I'd consider vibes. GIMP looks 'old'. I don't mind programs looking dated, but I absolutely mind them looking 'old' since that, to me, implies a worse experience compared to 'dated'. It looks like it crawled out of the education software setting intended for mass adoption and only barely did so.

To be more specific, things like proper spacing between UI elements & UI and text spacing go a longer way than I think most FOSS developers that don't work with UI expect. Everything feels cramped, like it is pressuring me to know what to do; there is a shocking lack of collapsible menu items and visual distinction is very low when parsing things like selected tool settings. Basic features are also somewhat unintuitive; when I go to drag a slider for opacity, for example, as an end user I don't think that single clicking and dragging will select the actual numerical value of the slider. I expect to have to double click, otherwise I expect the slider to simply do what I want it to when I left click and drag it left or right.

I don't think anyone reasonable expects to pick up heavily featured photo manipulation software and simply know exactly how to do as they please, but there are some surefire ways GIMP contributors can clean up GIMP's UI and UX. I mean no ill will by this, because people who contribute to FOSS do so with their free time and money, but I feel like a lot of software developers and highly computer-literate users think 'good enough to use for everyone I talk to' means 'ready for everyone to use' and this simply is not true. Talk to any 'normal person' in a somewhat young* corporate design environment, for example, and they'll probably scoff at you if you suggest GIMP measures up to anything Affinity or Adobe. Those people are dicks, but their attitude often comes from a place of valuable opinion. It is not keybindings or solid basic features that they feel is missing, it's... polish, I suppose? 'Completeness'? I'm unsure of the right word to use but something about GIMP just feels half baked, visually and feeling-wise at least.

And because it’s consistent. Gimp’s tools are random as all hell. It’s not just different, other tools have been designed by actual designers while Gimp’s community has been shooting them down for years. Leaving a confusing mess where shortcuts and tools have no obvious hierarchy or flow.

It’s cool it works for you but there is a reason everyone is able to learn Blender, Photoshop, Capture1, Resolve, Darktable, Krita, etc and suddenly get enraged at Gimp. I can’t think of any other project that gets this hate constantly. Darktable UI is rough too and the vibes are completely different. The Gimp community is toxic as fuck to criticism and it’ll be a miracle if there is anyone left willing to spend their precious time providing feedback. I’d love to see that change but I think as we see in the comments that many have moved on.