5 - 10 years back, Oracle was very far ahead of the database game and there was no practical competitor regarding performance, query optimization, storage management and enterprisey management features. For quite some time, if you needed a large central relational store for a business, Oracle was the only answer.
The main change is that MariaDB and PostgreSQL have caught up a lot of ground over the last years, so OracleDB has been losing the edge they have been paid for.