You need the centralisation for enforcement. And the centralised entity trusts other branches of itself, not the blockchain. The police and courts do call the county recorder if they need to establish whose ownership they're enforcing. If that centralised entity is corrupt enough to surreptitiously mutate records, immutable records that you've made arent much help

At best, the blockchain is superfluous, at worst misleading, since whilst the tangible benefits of ownership rests with what the county recorder says, you can sell notional claims to ownership of the property on blockchains to other people, potentially multiple other people all thinking their token on their blockchain is canonical. The priority of the enforcing agency is a much bigger issue for real world property rights than the mutation of records