I think there's a lot more than just cheap labor going on here... Newsflash to some, but the US is business unfriendly when it comes to industrial facilities.
Simply complying with building & environmental codes can double or triple the cost of a structure, and adds overhead into operations. God forbid you want to use chemicals to strip metal, or operate a paint shop.
Ever wonder why some railroads don't repaint their equipment very often? The EPA made it too expensive. It's cheaper to replace the equipment after it rusts out than it is to keep a paint facility licensed.
It's the same reason we import more and more of our refined oil products instead of building new refineries in Texas. It's cheaper to refine off-shore and bake the transportation cost into the retail price...
There's a balance to be struck between ensuring safety, and allowing companies to do business without too much interference. Big government fans haven't figured that out yet.