* Because most traditional databases are not designed to be decentralized.
* Because administrators by default can change data in databases. Of course you can work your way around that and get an audit for your solution. But it is a native feature of blockchains.
Let's say it is law pharmacies have to ensure each drug they sell was produced by a trusted vendor and rules regarding logistics (e.g. temperature) were respected. Nobody must be able to manipulate that data and it has to be available offline for all pharmacies in case the network goes down. It'd be almost trivial to set something like this up using a blockchain. In an early prototype, you'd just give each party one or more wallets (private keys), allow the pharma to mint a token for each package and track how those are sent between wallets, each representing a different state in the supply chain. Pharmacies run a full node to have data available in case anything goes down. I made it a bit easier here than it likely would be in reality, but I hope I can transport the beauty of the approach.