Listen guys I know a lot of people are complaining about Oculus going to Facebook. Carmack is a total genius.
There are a couple of reasons this probably happened.
This is from Carmack's message when he joined Oculus Rift as CTO last year.
I believe that VR will have a huge impact in the coming years, but everyone working today is a pioneer. The paradigms that everyone will take for granted in the future are being figured out today; probably by people reading this message.
Carmack probably started the ball rolling to get Facebook interested. Carmack has always had problems with massive user connectivity to his systems. He has never really been able to manage it very well or he would have pioneered a MMO. His focus has always been geared towards bringing fast paced FPS game engines to market but they almost always lacked very good latency or rendering when more than 16 people would join a game. Facebook has been working on connectivity since day one. Carmack probably wants them involved so he can access their complete knowledge base.
I think this is a calculated move by Carmack. He's also going to shake things up at Facebook.
I think he's gonna have a positive effect on Facebook and also on Zuckerberg, who has lacked a moral mentor that will possibly be found in Carmack.