I disagree. I use Affinity Photo 2, which also has a different interface, and it's so much easier to use than GIMP despite having more features.
A big problem for a chunk of possible users was that GIMP's colour support sucked (and I believe it's still not really fixed). The moment you wanted to work outside RGBA at 8bits per channel, and maybe a bit playing with indexed color, you were in for a lesson in pain. And a lot of people wanted a tool they could earn money with, and that meant for a long time at least some amount of print work. And print, even digital printing, means CMYK. Later on photography started demanding HDR features. Even web these days will deal with non-RGB color spaces, and I am not talking about HDR.
Meanwhile GIMP's engine for years even if in UI you technically could select colours in CMYK, they were internally converted to RGB for calculations, then converted again. CinePaint, aka FilmGimp, started because people could not get patches for 48bit RGBA into mainline. And so on, and so on. Meanwhile Photoshop and other competitors would not only have a less divisive UI, but also additional features (I knew people who would choose Photoshop just for included pantone colour database).
I'm not punching at all.
I use GIMP almost exclusively in my job. I have photoshop, but I know GIMP and I'm better with it. I make presentation pieces and fix images, do image data rescue and make fun pieces with it on the side, like posters for my bands and accidental art made by playing with sliders in the FX.
Its very versatile and capable, but it is almost entirely unlike photoshop, and since I grew up with it I vastly prefer GIMP over photoshop.