I actually wonder if proprioception has a lot to do with it. We pretty much use all of our senses with proprioception, and they are more limited by VR. No matter how good the eye tracking is, there will still be big blind spots and no matter how good the 3D sound is, it still won’t quite replicate how real sound moves between your ears. And then, of course, you have the illusion of walking without moving your leg muscles. This won’t change for a while. Not without major technological advances in VR gear.