Bingo. Had they made a better more modern UI, I think it would gain some traction. But they are entirely resistant to updating anything with the UI.
For me, and IMHO, every single one of them that I've seen is uglier than the original. For me, NeXTstep was the pinnacle of desktop UI design and everything else since has been less attractive.
Mac OS X was quite pleasing, if inconsistent, for a while around 10.4-10.6 or so, but now it's a mess. (I am typing on 10.14 right now.)
Win11 is a big less ugly than Win10, but the desktop is so crippled I find it hard to use, and there are ribbons everywhere. I hate the ribbon.
Win10 is kinda ugly but at least it's mostly black.
Win7 was and is a bit garish but it was the sweet spot.
XP was fugly.
Win2K was the high point for Windows, and everything before and after were worse.