The same reason why when you use Venmo you don't think "wait, why use USD at all if it's all a database?"
The truth is, the current financial system is just a large number of databases trying to sync with one another, and one of cryptocurrencies' goal is to decrease this amount of databases.
The truth is, the current financial system is just a large number of databases trying to sync with one another, and one of cryptocurrencies' goal is to decrease this amount of databases.