Your brain wouldn't be worth much without your body. You'd be surprised how much your body does. Think of typing for example. You couldn't do it without the exact nerve/muscle pathways in your hands. Hook up robot hands (even crudely modelled after your existing nervous/muscle/bone system in your current hands) and you'd basically have to relearn to do anything. You'd be a baby again.

I think you'd be surprised how much this applies to. Speech, even things like counting we rely on our bodies for.

That may be true of the body, although our nervous system in our body is quite large, not to mention the spinal chord. But it's certainly not true of the developmental environment. For one thing, simulating that would require simulated thousands of other human brains.