Microsoft has already answered this. Their React Native target for the windows desktop uses UWP.
Microsoft is pushing UWP as a capable desktop platform. AFAIK, they aren't ending support for their other platforms just yet. WPF is still being worked on last I heard. If you look at win10+, UWP is a perfectly valid choice for React Native. You could have React Native targets for WPF, win32, etc etc if you wanted.. I'm not sure what use cases could benefit from that though.
Keep in mind, if they're missing something in UWP that they need for React Native, they can add it to UWP.
Microsoft is pushing UWP as a capable desktop platform. AFAIK, they aren't ending support for their other platforms just yet. WPF is still being worked on last I heard. If you look at win10+, UWP is a perfectly valid choice for React Native. You could have React Native targets for WPF, win32, etc etc if you wanted.. I'm not sure what use cases could benefit from that though.
Keep in mind, if they're missing something in UWP that they need for React Native, they can add it to UWP.