There are several points that I want to highlight to answer your question.
Almost all distributed databases that are available today are fault-tolerant. But make a note that not all of them are Byzantine Fault Tolerant (BFT), meaning that they can not handle arbitrary faults. However, most blockchains are BFT, meaning that even if you don't trust some of the nodes in the blockchain network, you can trust the overall system.
Many distributed databases allow to change or delete data. Blockchains do not allow users to change or delete data because all transactions are recorded in an immutable ledger within the blockchain.
A central "admin" user can perform all operations in distributed databases, including change of data, deletion of data, deletion of entire tables or collections, or deleting the entire database. Blockchain is a distributed ledger, so that the central point of authority is not there. For this reason, any decision has to be taken in the consensus of nodes.
BigchainDb wasn't Byzantine Fault Tolerant until recently. Therefore, the database admin had the authority to do anything in BigchainDb. New BigChainDb version will be released as BFT, and therefore any single point of control would be absent.
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