You don't necessarily need to move anything other than eyes. It's the default input method, but it doesn't require it. It's a computer, it can connect to other devices or use APIs.
So if you use a headset meant for spatial movements, but you're unable to do spatial movements, can't you just use a display and get exactly the same experience?
A very close experience yes. It works just fine with zero head movement and you can move and adjust your windows to only be directly in front of you. And they are by default