My own personal outsider take on this is that there are really only three eras that need to be considered:
- "HWND era": win16/win32 classic UI aka "WinForms". This extends all the way up to ActiveX. Microsoft get to dictate the platform without real competition.
- XAML era: the second system. Classic WinForms doesn't handle high-DPI displays or GPU rendering; it relies on pixel positioning and lets you draw directly on the framebuffer. WPF is the reaction to this.
- Phone era: suddenly there is real competition and users start using a lot of non-Microsoft platforms. Microsoft launch their own phone, complete with new sandboxed APIs that don't correspond to Win32 at all. This is ultimately a market failure. But Microsoft have invested too much in UWP.
At this point, the winning stacks globally are, in order: web (including Electron), iOS, Android. Nobody wants to do native Windows applications that aren't games if they can possibly help it. Even Microsoft start building web-on-desktop apps like Teams.
So the only thing Microsoft can do is salvage operations on UWP APIs and XAML-related techs to try to make it usable to desktop developers by getting out of the sandbox.