because your eyes are looking straight ahead for the most part. It's like seeing the world through a narrow view point like binoculars (sans magnification).

You can dart around within that narrow window, but mostly you are looking around by turning your head. You are subjected to more visual motion than you would in real life.

Your eyes still saccade when you turn your head. If your headset is causing your eyes to stop saccading properly, I'd expect that means it's not rendering fast enough. I also don't see how adding jitter to the turning would fix this. That seems like it would just cause major disorientation. Maybe I'm totally off though.

I was at the mall and had a chance to try out an occulus rift. It was a very pleasant surprise. My speculations were completely wrong, it felt very natural.