How so?
Their one big exclusive deal this gen (so far) excludes the PC platform (although this deal is timed so it will be coming eventually).
Forza, despite being shown running on a PC initially at e3, and being used as a proof of concept for DX12 when it was announced, still hasn't been released or even been mentioned as something thats going to happen.
Lets go through the list, Forza - No, Halo - No, Tomb Raider - No,
Crackdown - No,
Crimson Dragon - No,
Gears of War 4 - No,
Quantum Break - No,
ReCore - No,
Sunset Overdrive - No, OK I'm boring myself here.....
Other than an MMO, I cannot see one game created by a first party MS studio that is going to appear on PC.