> why should it be cheaper to run a robot factory in China vs. the US?
Among other reasons, there's: 1) cheap utility inputs, mainly hydro/coal electricity and water; 2) laxer environmental standards; and 3) remaining labor needs are still cheaper.
Also there is a lot more general infrastructure and expertise in manufacturing a lot of product types there. And no doubt the factory making the robots will be down the road, improving the ecosystem. Generally you do not do every process in house so you need component suppliers and specialist process makers nearby.
Reindustrialising the US and Europe would be hard.
Among other reasons, there's: 1) cheap utility inputs, mainly hydro/coal electricity and water; 2) laxer environmental standards; and 3) remaining labor needs are still cheaper.