I feel like the Japanese found the goose that lays the golden eggs (private trains with real-estate/hotels/supermarkets/shopping-centers). The parts form a virtuous cycle where better trains = more people come to use those other things, and those other things make more people take their trains. As such, the government doesn't have to fund the train systems and so they're not chronically underfunded like they are in so many countries.

And yet, no one will copy them. There's always some excuse. LA is going down the excuse route and adding train lines with no chance of ever supporting themsevles. They are all designed as a handout to the people who are too poor to buy a car, rather than viable alternative to cars, and the fact that they aren't connected to all of those extra things means they'll also never be as compelling to use.