First of all, You've never worked at a corporation? Sounds like it. Corporate politics can easily eat-up an individual influence on the direction a product goes. Especially when you're judging long periods of time, like entire history of Oculus from the looks of it.
Second of all, go read his public rant after resigning. you will find answers there.
I'm sure the rant is interesting. I haven't really been following his life story.
I suspect that when Carmack was making PC games all the way from Commander Keen to Rage, he understood the value of PC as a free/liberated platform. Do I have proof? Well, here he is lamenting the consequences of working on a proprietary platform. I'm content with that.
This isn't some kind of trial. My point is not to condemn the man. My point is to use his character to articulate the story of my own perspective.