The fragmentation is a huge reason the desktop experience is broken. The only UI that's actually consistent across all distros and works pretty damn well is the TUI.
Its not fragmentation, you (and others) just do not grasp the very basics of Linux.
Its open source.
We will never, and I mean never, have one desktop to rule them all. That's impossible. Not improbable, impossible. You just can't make that happen on Linux.
What you want is a closed-down ecosystem in which one actor controls it with an iron fist. Which is fine - more power.
But we already have that. That's windows and mac os. If Linux tried that, it would destroy it.
