Ehh...this is essentially an attempt at making a killer app for Windows phones and Windows powered tablets like the Surface. The PC release is pretty much incidental.
Microsoft's Halo 2 release on PC was a disaster. I mean like it came out 3 years after the game's console debut, it was only compatible for DirectX 10 and up in an attempt at creating a lure to get people to upgrade, and of course it was released on the crap GfWL. So yeah it was a big enough bomb to convince Microsoft to skip porting every other iteration of the series onto the PC, even Halo Wars that RTS that Microsoft had Ensemble Studios make before shutting them down.