The bearings in trains are actually pretty complicated to build. They use slanted roller bearings, not just regular old ball bearings. 10 companies in the world make like 70% of all rail bearings, and 5 of those are in Japan. Plus, only a few countries produce the two steel alloys that you make these bearings out of.
China does produce around 20% of the bearings used in trains, but pretty much all of it gets used for domestic purposes and they still have to import due to their massive rail expansion projects