Sure, KDE is in itself more coherent than the Windows DE. But the point is that there's only one DE for Windows. And even if it's incoherent there's just one to develop for.
But there isn't just one to develop for... There's over half a dozen loosely connected design patterns over time. You have win32, the office/win 2k expansions, the modern ribbon, winui, winforms over win32, and now fluent, and Maui. All depending on what you're writing in and targeting.
It's not significantly better and combined with Mac and Linux a large reason many apps are using a skinned browser engine. You get better developer ergonomics for scaling, languages, screen readers, general accessibility and portability over many dedicated UI component libraries.
MAUI could have seen massive adoption with a Linux target (even if just gtk). It's not the biggest in terms of users, but it's become very large in terms of developer mindshare. Without it, it's an also ran.
I'm not a fan of gtk or QT. I don't really care for the shortcomings of most options at this point. Everything kinda sucks. Skia may gain traction and patch the missing pieces, but who knows.
Right now, when is the only mostly safe option for cross platform general desktop apps. Which is weird.
Linux has hundreds probably, maybe more.