Why? There's not many that actually do unique things. KDE/GNOME are the big ones, then plenty of macOS clones without much substance (i. e. Cutefish, Pantheon), the lightweighter Windows clones that all somewhat work the same (Xfce, LXQt, MATE, Liri), and that was basically it. They all do the same thing Windows or macOS do, featuring the same design choices and look and feel; oh look, a full-size taskbar with a clock in the right corner and a start menu in the left corner! Riveting.

The only ones that really have something unique going for them are Trinity, WMaker/GNUstep, Enlightenment/Moksha, CDE, EMWM and maybe Sugar. You'll notice that they're not exactly the most popular or well supported ones.

Where's really creative and innovative ones like ROX used to be? Where's the funky 3D desktop environments? Where's ones with completely new control schemes like a radial menu or a modern take on iconification? Where's dockapps? Where's innovation?