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.
My longest single day non-stop drive was around 18 hours.... Never even left the province. The flight alternative required me chartering my own plane and would have cost many many thousands of dollars more, so I went with driving as it was the cheapest option.
As a European, these distances are mind-boggling. If I drive 18 hours, I can drive through half a dozen countries (or more, if you optimize for that) and easily get from the Baltic sea to the Mediterranean sea.