All I can say, is my dad recieved a hell of an offer to return (and so did his buddies). The people he trained all had PhD's from various universities around the globe and were supposedly excellent material science engineers. My dad had a high school education, but was trained/worked for decades in this particular field.
The molds that make every component in a MacBook need to be better than those assembling them. The skill to plug in a keyboard or even run a machine to make a keyboard, is not the same as designing or creating the molds of the keyboard. Apple does all of that (to my knowledge) in the U.S. The reason is likely security of their IP and that they have a critical mass of skilled people here, able to out perform elsewhere. Also, it's easy to ship designs anywhere, not so much material goods.