I think exclusivity is dumb, but come on. You know why. Because Microsoft probably paid them.
It's the same reason Crystal Dynamics isn't going to post a blog post saying "oh by the way that Xbox conference was bullshit, we actually are releasing in 2016 on other platforms" the day of the Gamescom announcement. If Microsoft did pay for timed exclusivity, part of that is the additional PR you get from saying "the game's only coming out on Xbox One!" You can't just turn around and say "actually it's not" because Microsoft wouldn't like it.
That said, this is why I hate timed exclusive announcements like this: because it's bullshit for the consumer. Imagine going out and buying an Xbox One because you heard the next Tomb Raider game would be exclusive, only to find a PS4 or PC version was actually coming a few months later. You'd be pissed if you spent $400 or $500 you didn't actually have to spend. Granted, there might not be that many people in that position, but whatever. It's cheating people out of money.