John Carmack was the heart of id Software. He's one of the most well known developers out there and the news of him leaving id to join Oculus sent shockwaves throughout the industry.
It wasn't known why he left until now as an interview with USA Today revealed that he left id because ZeniMax Media, parent company of id, wasn't interested in VR. They didn't do a deal with Oculus where John could work on one of his dream projects and provide official support for the Oculus Rift in Wolfenstein: The New Order and Doom 4.
John would have been happy to split time between the two companies if a deal was done between Oculus and ZeniMax, but seeing as there was no interest in ZeniMax and he was wanting a new challenge over programming games for the console or PC. The Oculus Rift was that challenge and he decided not to renew his contract with id Software.
John might be right when he says VR is the next big thing. I was blown away by the Crystal Cove edition of the Oculus Rift at CES and I'm anxiously awaiting the time that I can order a consumer version of the goggles. Now with John on board full time, there should be some big developments coming out of Oculus at a faster rate than before.