There is, in fact a reason we can't replicate that
today, and it's not for lack of trying. We don't have neither the full understanding of the human machine nor the technology to replicate it. As an example, muscles are well-understood, but we haven't been able to make artificial muscles with energy efficiency in the same ballpark. The human brain is much less understood.
I'm not saying it won't be possible at some future date after some hypothetical breakthroughs, but we are far from it presently.
