UWP requires a non-standard compiler if you want to target it from C++; a non-standard C++ compiler is not required for UWP because it was always mainly for the C# crowd.
Microsoft not only could be better, but is: C++/WinRT is the standard C++17 way into WinRT, provided as a header-only library for any old compiler.
Alas, I have absolutely no idea how UWP maps to WinRT, how either corresponds to Win32 or .NET, or what WPF has to do with any of it. All I really know is: don't mention Silverlight.
I think Reunion is meant to clarify, even to idiots like me.