I think it's two things:
1) sony are leading the next gen as they did with the last, so they are further down the pipeline.
2) MS is trying to learn as much as they can about the ps5. They've already changed plans according to rumours from two next gen models (one being super powerful), to just the one. They might change their mind about vr again and they don't have the confidence sony do with their hardware unless they can call it a beast or the most powerful.
They lack vision and confidence. Sony at least knows what they are making, why and what purpose it will serve. You can't plan properly by just waiting and anticipating, you need vision and planning too.