Microsoft has written more application development frameworks than you can shake a stick at. They've also failed to gain traction with virtually all of them, even internally.

Leadership is weak.

As an operating system vendor, it should be a dismissable offence to refuse to use the OS standard APIs. Your products need to be the standard that other try to imitate.

WinUI2/UWP was heavily adopted internally though?* Most Windows shell UI and built-in apps use it at this point.

* (at least within the Windows organization; maybe not so much in other parts of Microsoft)