Many do it, including Russia. It's not quite that simple as in reality there are many tax incentives in play. In the end the lost tax revenue might be greater than the benefit to workers (and tax revenue from that). I remember reading this is the case in US but I don't have the article at hand.
China and Russia are different animals, both have an abundance of workers who will work for very low pay. X-series BMWs are luxury items so that manufacturing in US won't matter if it adds to cost. For anything price sensitive, say watermelons (case of fired Mexicans in Georgia), things are different - you can't even fill the positions.
US can become completely isolationist and then people will pay whatever price is charged but does anyone realistically want that?
You're wrong about BMW selling the cars made in South Carolina locally:
BMW Manufacturing Co. announced today that the export value of its passenger vehicles through the Port of Charleston in 2015 totaled $9.8 Billion, confirming the company’s South Carolina facility as the leading U.S. automotive exporter by value. According to data from the U.S. Department of Commerce, this accomplishment represents a 7.8% increase over BMW’s 2014 value. In 2015, more than 280,000 vehicles were exported from its South Carolina plant, over 70% of the plant’s total volume.