From the top of my head I can think of a few reasons:
Better feature support (HDR, better fractional scaling etc)
Better integration (specifically Gnome)
More complete graphical settings
Quicker adoption rate
Wayland support (X11 is pretty much dead at this point)
Aside from RAM (of which most machines do have plenty by now) there isn’t really too much overhead these days. In fact battery usage on Gnome and KDE with Wayland is usually better than with X11.
From the top of my head I can think of a few reasons:
Aside from RAM (of which most machines do have plenty by now) there isn’t really too much overhead these days. In fact battery usage on Gnome and KDE with Wayland is usually better than with X11.