China has high speed rail in its eastern most populated section, with a single line running to the entire western half of the country, and similarly sparse lines to the north. The dense population centers in the US are not all in one area, they are spread across the continent interspersed with large swaths of rural land. That being said the US is working on high speed rail, and we've had passenger trains that cross the entire country for nearly two centuries - see Amtrak, as well as bus services like Greyhound.

As much as I hate to break up a circle jerk, the US is about as good at this as any other western country, and it's doing it across an entire sparsely populated continent, not small, highly dense European countries.