They also have a very good motivation to build the infrastructure, this is a general phenomenon i tend to refer to as the "big city effect".
When you have that many people and that much population density it becomes incredibly difficult for governments to sit on their hands, because it's obvious to everyone that new infrastructure is needed.

Which makes the US look so much worse. By all means the big cities in america should be decent places to live purely by dint of population, but the government has spent decades trying as hard as it can to make things as shitty as possible.

Australia is roughly what i'd expect america to look like without an active conspiracy to make it shitty: Largely empty, the cities are far apart and very suburban, but the cities have local downtowns spread throughout and it's all connected with trains or at least buses.

Well, the perk of being an authoritarian regime is that you don't really have to put the high speed rail on farmland. Urban blocks are fine too if it's a better path.