Different situation across different sectors of Japanese railway too. But the big thing across privatised asian systems* is business diversification, especially if they're set up to survive on their own. The other part is critical mass by passenger numbers - loss leaders aren't a big thing iirc and the railway business on its own can make money, but they're often part of larger groups (Hankyu, Seibu [lol tsutsumi], Odakyu, Keio, etc) which also tend to make money.
JR is a special case because it was like washing away the old pain in that the big 3 formed with silver spoons after privatisation. The big 3 JRs also make money while the others suffer a bit (JR Hokkaido suffers a lot).
The diversity is pretty broad too. JRs can do their own beverages and water, hospitals, farms, in house rolling stock design (down to small details like custom network connectors) and construction, infrastructure design, etc.
Also the role of the railway in society. Everyone takes the train at some point.
Someone else who knows US rail better can chime in, but they do move fuckloads more freight than anyone else and non-human cargo doesn't complain as much, nor does it require air and water (usually).
*You're allowed to laugh at the mess that happened in Singapore though.