False. China has high-speed trains that travel around 1000 km. China is also big. Really big. Also pretty poor. But it manages despite its ridiculous dictatorship to get a modicum of useful stuff done. Stuff that the US--uniquely in the democratic, developed, world--is unable to do.

For more information: https://en.wikipedia.org/wiki/High-speed_rail_in_China

So the claim that "trains don't scale well in the USA" is false. Trains scale just fine to thousands of kilometres. The distance from Bejing to Hong Kong, which has a rail line capable of more than 300 kph (https://en.wikipedia.org/wiki/File:Rail_map_of_China.svg) is just shy of 2000 km as the crow flies, which is more than the distance from NYC to Chicago and a bit less than the distance from NYC to Dallas.

And pointing out that LA is more distant from NYC than that is utterly, completely and totally irrelevant. The distance from NYC to LA has absolutely nothing to do with the inability of Americans to build a high speed rail link between various Eastern and Southern cities, and there is zero plausibility to any claim that NYC and Chicago (or Dallas) aren't commerical hubs of comparable importance to the US as Bejing and Hong Kong are to China.

So we can put that false claim to bed now, and never muddy the discussion with it again.

The more plausible reason is the other one you cite, at least by implication: the American economic and political system, uniquely amongst developed democracies, is unable to muster sufficient collective resources in the form of public or private investment to enable creators to build a fairly straightforward rail network that would serve American economic needs.

The US is not "the most technologically advanced coutry in the world". It is two countries, one of which is technologically advanced, the other of which is backward in almost every respect (and kept that way by policies set by the first.)

Until Americans figure out how to deal with their unique social and political deficits and inabilities they will continue to suffer under stub-standard conditions in almost every respect. They will continue to die earlier, live with higher crime rates, lousy railways, and dramatically lower economic efficiency than that enjoyed by citizens of almost any other advanced nation.

Canada also sucks with respect to passenger rail, and we are generally far better than Americans at solving our collective problems, so there may be more to it than that, but clearly size alone is not the issue, or China wouldn't have the amazing high speed rail network it does.