Facebook can try to ensure that the games are geared towards social interactivity that benefits their platform, but in the end, the developers truly pick the direction. Anyone can buy a dev kit and see what they can build with it.
Maybe Facebook wants Oculus Rift to operate as a completely separate entity outside their core business. Maybe it's something they believe in and want to expand into a new genre. Mark has some interesting insights on where to take it: https://www.facebook.com/zuck/posts/1010131905052397.
Think about when Microsoft got into gaming and created Xbox. Now imagine if they didn't.