Most of the games that went to PC were never Microsofts to port. They didn't reach their numbers so they went multiplat. Fable Legends and Ori and the Blind Forest are the next multiplatform games, but so far thats five (including Titanfall, Ryse and Dead Rising 3). All three of the other games I mentioned were never Microsofts to give.
Much like the original Xbox a lot of good exclusives between the PC and Xbox will be shared, but that doesn't mean those are the best games.
How do you know they didnt reach their numbers? maybe it was planned?
There were reports talking about disappointment in Ryses numbers and there were rumors that Crytek had interest in putting the game on the PS4 as well. Dead Rising could've been planned but I am willing to bet they had to expand to make more money on a platform Microsoft wasnt really obstructing them from launching on in their contracts. If you remember before, Dead Rising 2 was on the PS3.