It's because of their outstanding selection of exclusives. Something that Microsoft (and to a lesser extent, Sony) didn't see. Also, I'm pretty freaking sure that if Halo 5 was actually worth buying, it would have rocketed their console back to greatness. But they screwed that up. They screwed their exclusives up. And now they're paying for it.
I actually don't blame Microsoft though at all for trying to get rid of exclusives. They simply wanted to get rid of the fact that you had to get one specific console to play one specific game. An admirable goal to be sure, but the sad truth is, exclusives are a necessary evil. Although there are some benefits to gamers and devs by making console-exclusive games. It means less headache for the dev and more of an ability to optimize the game for one specific piece of hardware, which leads to being able to make a particular game better on one system than it would be if it had to be ported across three sometimes radically different consoles. And finally, it's good for the console-makers themselves obviously since it moves units and builds brand loyalty.
I actually don't blame Microsoft though at all for trying to get rid of exclusives. They simply wanted to get rid of the fact that you had to get one specific console to play one specific game. An admirable goal to be sure, but the sad truth is, exclusives are a necessary evil. Although there are some benefits to gamers and devs by making console-exclusive games. It means less headache for the dev and more of an ability to optimize the game for one specific piece of hardware, which leads to being able to make a particular game better on one system than it would be if it had to be ported across three sometimes radically different consoles. And finally, it's good for the console-makers themselves obviously since it moves units and builds brand loyalty.