First, humans are still necessary - to build the factories, to operate them, to act as security guards - and the cost of those humans is still lower.

Second - all the other costs in low wage countries are also a lot lower. Combine that with how absurdly cheap international shipping is and there is no reason to relocate the manufacture of low-margin goods to the US until you are really starting to talk about the costs of automation being so efficient the extra pennies on shipping will make a difference in earnings. Given the expense of maintaining real assets in the U.S., i.e., buildings (utilities, maintenance, insurance, taxes, building), this is likely to be a while.