It ain't. The logistics of it just don't add up. We're already running out of non-renewable lithium, copper and gold just making cars as it is. And that's just for making the parts in the first place. You know how expensive it is to maintain a car? Now imagine just how tough that would be with a machine that has wear and tear 24/7, not to mention the body rejecting parts.
As much as some pyschopaths jerk off to the thought of enslaving humans with chips and such, its just a fever dream.
Biological modification on the other hand is much more fiscially possible.