IMO, and IME, the secret sauce is their education curriculum.

Japanese schoolteachers and the Japanese school curriculum spend a lot of time drilling correct social behavior in the classroom. You are socialized to obey the rules. You are socialized to think its bad to not follow the rules. You are socialized into being cohesive with the group.

I mean there is more to this. Their society as a whole has decided this is an acceptable task for schools to undertake and participate in it actively. But it’s the machine that keeps it going.

Also bullying is a feature not a bug, despite all modern attempts to squash it.