>>133070
It's not the only thing many of the companies make. Selling rolling stock internationally is really just icing on the cake for many of them as they rarely get really big contracts, just little bits here and there. Now that Tokyu Car Corporation is pretty much part of JR East - they do their rolling stock in house top-down. What little external hardware there is, is either sourced externally because they can't do it in house, or for shits and giggles. As a topic of personal interest, this was a thing with the air conditioners used on some trains. JR East can do them in house via TransporTec but they get some (of the same design, mildly different in appearance) from Mitsubishi Electric anyway. Same thing with Hitachi trains which some do use Hitachi aircons but some also use Toshiba units. Or the N700 which uses aircon units from both Toshiba and Mitsubishi Electric - except they're pretty much identical in spec and appearance.
In the inverter space, it's really just Hitachi which is self sufficient. And with bogies, it's everyone supplying everyone.
Others like Alna Sharyo though are just small makers and probably get by likewise. Beyond that, they also get money through constant rolling stock programs.
Curiously, the domestic cost for Japanese rolling stock is relatively cheap. Considering the Alstom garbage thrown at us here (lacking even the basics such as air spring suspension because the government cheaped out) costs as much as a Shinkansen per carriage, I'm always left amused and appalled at how the government lets itself get gypped.