China has 160 cities with over a million people whereas the USA has only 10.
Further, the USA has 263 million registered cars, whereas China with a far greater population has 244 million.
Means a lot more people need mass transit in China than the US, and a lot of people are concentrated in large cities.
While I don't disagree with your point in general, I think that 10 number is rather misleading.
My address is in Tampa. I get my water from the City of Tampa. If you drove all three miles from the Tampa airport to my house, you'd never notice that you left the city limits (there was a sign marking the border going the other way at one point). But, I don't live in Tampa. Of the 4 million or so people in the Tampa/St Pete area, less than 400,000 technically live in the Tampa city limits.
Then there's Jacksonville, the largest city in FL (though still less than 1 million). When I drive up that way I pass the city limits sign before I pass the county limit sign. And I'm still about 40 minutes out of town.
So, I guess it depends on how you measure.
Oh, and trains still suck, at least around here.