Why would development time be wasted? Most of these forks are "I like the basis, but I want to tweak it a bit". To each their own.
I suppose Unity was a bit of a waste now that it's been mostly abandoned for standard Gnome these days. Then again, Canonical has a history of starting forks and alternatives and releasing them early, eventually ending up replaced by competitor projects that learned from their mistakes.
The fact KDE's design hasn't inspired much in terms of forks seems like negative signal to me. Very few people who want to implement things their own way seem to be using KDE as a basis. I don't know if that's because KDE is more difficult to work with or if KDE people just aren't the ones that like to experiment with their own vision, but nobody forking the project is not necessarily a good sign.
That said, KDE did just finish a complete redesign, with a Gnome-like desktop switcher, a Gnome-style (or rather, macOS-style) dock, altered default behaviour for mouse clicks, touchpad taps, and the way scrollbars work. Perhaps it'll inspire the next generation of tinkerers now that the redesign is out.
KDE gives you the freedom to do whatever you want with it that's why they don't need to be forked. They actually learned from their community after the backlash they got for kde2. Oh and also gnome has no dock...
That said you seem to misunderstand the gnome "workflow" if you think the new KDE features are copies or similar to the gnome workflow™. I give you that they are visually similar but most of the concepts you described were shaped by xerox.
Valve chose KDE for SteamOS, including as the desktop mode on the Steam Deck, a device sold to be so user-friendly that it can compete with home consoles including the Nintendo Switch. (Not saying that desktop mode itself is as foolproof as a console interface, just that it can't be a total usability disaster for people who bought a Steam Deck for gaming and not as a Linux desktop)
Emphasis on chose KDE, not forked KDE. I agree with people who say that KDE has gone to great lengths to be customizable enough that you can mostly set it up the way you want without forks, extensions, or even registry editors.
I can't speak to how difficult Valve found it to work with KDE, but it says a lot that they still chose it overall. It's not often we get such a clear positive signal from a company that invests so heavily in user experience.
I suppose Unity was a bit of a waste now that it's been mostly abandoned for standard Gnome these days. Then again, Canonical has a history of starting forks and alternatives and releasing them early, eventually ending up replaced by competitor projects that learned from their mistakes.
The fact KDE's design hasn't inspired much in terms of forks seems like negative signal to me. Very few people who want to implement things their own way seem to be using KDE as a basis. I don't know if that's because KDE is more difficult to work with or if KDE people just aren't the ones that like to experiment with their own vision, but nobody forking the project is not necessarily a good sign.
That said, KDE did just finish a complete redesign, with a Gnome-like desktop switcher, a Gnome-style (or rather, macOS-style) dock, altered default behaviour for mouse clicks, touchpad taps, and the way scrollbars work. Perhaps it'll inspire the next generation of tinkerers now that the redesign is out.