My guess is that it's two things: To get developers to use Windows again and to get developers to use Azure for everything.
Not quite true; Android Studio has some tools to help you get a mobile backend onto Google's cloud.
For the front end, this probably won't have much effect. Developers go where the users are and there's very little excitement around Windows applications (win32 or universal). If keeping developers happy was all that important, then Linux would be the dominant desktop OS.