UWP apps have a lot of limitations compared to WPF/Win32 apps. As I understand it, UWP apps can't record audio in the background or act as a Bluetooth accessory, to give two examples.
So, even if a developer is willing to invest the time to rewrite an app to use UWP, the app will lose a lot of functionality. Microsoft has again poorly architected their APIs.
Unlike macOS, where there's no penalty to adopting the latest APIs. It's not as if, to use the Touch Bar, you have to give up access to other capabilities, like recording audio in the background.
I mean, you can just use WPF + the desktop bridge in these cases. There's still some work for the desktop bridge to catch up, but it's perfectly feasible (aside from, you know, feeling like a traditional Windows desktop app vs a "Modern" one without a lot of work styling WPF controls).
So, even if a developer is willing to invest the time to rewrite an app to use UWP, the app will lose a lot of functionality. Microsoft has again poorly architected their APIs.
Unlike macOS, where there's no penalty to adopting the latest APIs. It's not as if, to use the Touch Bar, you have to give up access to other capabilities, like recording audio in the background.
More information: https://kartick-log.blogspot.in/2016/08/how-powerful-is-uwp-...