Database can be modified, managed and controlled by administrators. There are always administrators for database who will have full control over the database. They can create, delete and modify any record in the database. They can optimise the performance and size of the database. The larger the database the slower the performance will be, so the administrator can take various methods to optimise it. The administrator can also transfer this access to someone else. So databases are centralized.
Blockchain is a decentralized distributed network architecture. There is no need for a centralized database, all the nodes of the network are connected to each other. So no one can control all the nodes and there is no need for an administrator on the blockchain. What if one of the nodes is fraudulent? Would this affect the whole network? The theoretical answer is that if they get most of the computing power, then it is possible. Theoretically, if someone can control 51% of the computing power, they can control the network. This requires a very large amount of computing resources, so it is very expensive to generate an attack.
So if fraud needs to be committed, all the nodes in the network would need to be changed. In reality, this is something that requires a lot of computing and power and is very difficult to accomplish. It's a way of regulating, in order to make sure that nobody can defraud anybody. This is why the blockchain is immutable. At the same time, the blockchain is transparent because the transfer information can be seen by anyone.