if we need centralized enforcement and off-chain enforcement, anyway, what actual value does a blockchain add compared to an access-controlled database?

Enforcement of laws and documentation of ownership are two separate functions. Blockchain does the former only if everything is digital (like money).

Let's take licence to drive as a pure real world enforcement example. There are multiple countries so there are multiple centralised databases. Blockchain allows all those databases to be merged without needing central access control