well that sucks america is low (time to move to Japan lol)
Not quite . . . its robots per 10000 human workers, not total robots. The US gets a lot of low-wage immigrants so it definitely reduces the financial incentive to have more robots. Japan on the other hand only allows high-wage immigrants to move into the country - you need a minimum of a college degree to immigrate to there. No one with a college degree will accept low wages and manual labor!
Now if you saw a graph representing the number of robot research papers published per country, you'd see that Carnegie Mellon University alone annually produces twice that of the entire country of Japan. Represent!