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).
No. There are no passenger trains worth speaking of in the USA because the car industry likes it this way.
China is a very similar size to the USA and has an excellent and extensive high-speed rail network.
The USA could have this too, if it wanted to, but it doesn’t.