The feeling of presence is so limited compared to realtime-rendered 3d spaces where you can move your head around from the central camera point even just a bit. Adding some artificial parallax shift to the movie frames might be enough to give it that extra oomph to feel truly immersive.
The Oculus Go doesn't have 6 DoF, and he's been working on that and phone-based VR for the last few years. Because they're cheaper, they move a lot more units! And because they're more constrained, they need more optimization attention from someone like Carmack.
