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
At least KDE is planning to introduce customisable trackpad gestures next year, with Plasma 6.0. Not sure if that would include palm rejection though or the other stuff.