The answer to that is relatively easy, WinUI 3.0 being shoved into Windows, even though UWP has failed to get adoption, after so many reboots even those of us that were deep into it got pissed off and moved elsewhere, leaving the Windows team as the only group of folks still trying to push it.

Go have a tour on Github for the endless collection of issues, some of them 5 years old, when Project Reunion was announced.