It’s mostly libinput. Why the hell can’t I easily change scroll speed on Gnome and not on KDE? Why does gnome have a simple tool (gnome tweaks) to change the trackpad cooldown to change the time trackpad doesn’t work as a substitute for good palm rejection and KDE doesn’t? Why is it a bit of a pain in both to change trackpad gestures? Why am I hearing again about God damn redesigning the settings placement on most desktop environments.
Edit: I love both KDE and Gnome, and I think that they’re great. But it kinda hurts to see them fail on what seem like relatively simple things
You’re using software that’s being continuously developed by people for whom stability of the UI is not a priority. Pointless UI churn is normal. Half-assed solutions kept beyond their best-before date are normal. Windows does this crap too. At least with Linux you have a choice of which issues you’re going to tolerate (or you can pick a DE where UI stability is a priority for the development team).