WSL lets people run their Linux apps with Linux GUIs on Windows. It makes Linux apps cross-platform, which makes sense if your business proposition is "literally all software runs on windows, and some software also runs on non-Windows. Choose wisely"

And, IIRC, .NET Core doesn't support WPF forms for legal/trademark reasons. But other MSFT supported .NET Forms libraries that happen to be API/feature compatible work on Windows/OSX/Linux/Android/iOS.