America was built by train too to be fair

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.

Yeah, but they're making it for ideological reasons, and get to drive those rails through whatever territory they want without having to take opinions or profitability into account. Companies in the West that build rails have to do so profitably*, and with consent from the locals, both of which are major hurdles.

*Except in the UK, where they can piss away as much money as they want and get constantly propped up by the taxpayer while simultaneously paying vast sums to executives and shareholders.