That would only work if the scene was a single flat surface and you were only moving in parallel to it. If you were doing that you may as well not use VR and just look at a normal monitor. Otherwise it wouldn't match your motion, which is the problem you're trying to solve in the first place!
Actually moving parallel to it would make the artifacts worse as it'd distort the projection based on distance (i.e. parallax). With a rotation if you're rendering it onto a sphere, doing that rotation will have a very little amount of distortion from it comparatively. It still needs to be rerendered to be correct but this can allow for better intra-frame changes (say game runs at 60 hz, and you need 120hz) with less computation. As a sibling (to you) commenter pointed out, this will make the image slightly "fuzzy" or softer because you end up moving the image on a fractional amount of pixels. As I understand it though, that extra intra-frame can mean the difference between some people getting a VR migraine or not.
