Large roller bearings are actually pretty difficult to produce cheaply and reliably at large scales. I don’t really see this as being unbelievable considering 75% of all bearings used in rail are produced by 10 companies in Japan, the US, Germany, and Sweden.
Creating a production line completely in house and at a scale that would be sufficient to supply one of the largest rail networks in the world be a Herculean task for just about any country.