Short answer: cities are too far apart and the USA is large. However, how much funding is there to really implement the same thing that exists in Japan but in the United States? Also, is there an incentive for that in the first place? What about population density? Japan is more compact regarding their population density while that’s not the case for America plus both Osaka & Kyoto aren’t too far from each other (but Miami & Washington DC are distant).
my guy, the usa was built on the shoulders of a robust railway infrastructure.
the reason why it wouldn’t work is because the automotive industry has absolutely ruined everything and people have been conditioned over many years and multiple generations to regard any form of public service and infrastructure as “bad”, “pointless”, and “for poor people”, and so any attempt to actually modernize and fix any of these issues caused by car-dependency is quickly shut down by the ignorant.