China and Japan aren't exactly low-cost construction countries. Actually, they're among the highest-cost non-Anglosphere countries (which are perhaps best labeled "stratospheric-cost" countries). Instead, you want to look to places like Spain, Italy, Sweden, or South Korea as low-cost countries.

Their costs are lower because their land aquisition costs are lower. The problem isn't the tech it's the regulations/property rights.

Yeah, just bulldoze some houses and apartment blocks, so easy to build rail lines. Why didn’t anybody else try this?

Exactly this -- plenty of other countries have figured out how to build rail systems without massive cost overruns.

The expensive part is addressing all the local regulations and acquiring land.

Human rights (and property rights) can be expensive.

Well good ideas from capitalism does not apply to public projects did you not know?