That can be customized a lot (instead of the Gnome mindset of "Do on my way or fuck your self"), and run fast even without 2d/3d acceleration (aka the old good X11 SVGA driver ) ?

PD: Add that anything based on Qt can handle faulty graphics drivers far better that Gtk3.

And KDE 4 wasn't realized exactly with the mindset you describe with so much candor? Now Plasma 5 can be more flexible, sure. But when you don't give users a usable alternative for years people tend to look for alternatives.