There are so many areas where the various desktop environments should be collaborating, but aren't. KDE, GNOME, Xfce, and Cinnamon all have menu item extensions, yet they are wholly incompatible, forcing every one of them to create their own reinvented wheels. At least the GTK environments should have combined and standardised their efforts here over a decade ago (KDE would be harder to integrate here because they use Qt).
Users should come first. This is such a no-brainer.
So the number and quality of extensions will continue to be very limited for all of them.
At least, until somebody does for cross desktop extensions the same others did for cross-environment applications: find a way to wrap up a kind of browser extension as a very wasteful cross desktop extension. Are we ready for +100MB desktop extensions?