But here’s the thing — “private blockchain” is just a confusing name for a shared database. The key to Bitcoin’s security (and success) is its decentralization which comes from its innovative use of proof-of-work mining. However, if you have a blockchain where only a few companies are allowed to participate, proof-of-work doesn’t make sense any more. You’re left with a system where a set of identified (rather than pseudonymous) parties maintain a shared ledger, keeping tabs on each other so that no single party controls the database. What is it about a blockchain that makes this any better than using a regular replicated database? Supporters argue that the blockchain’s crypto, including signatures and hash pointers, is what distinguishes a private blockchain from a vanilla shared database. The crypto makes the system harder to tamper with and easier to audit.

https://freedom-to-tinker.com/blog/randomwalker/private-blockchain-is-just-a-confusing-name-for-a-shared-database/