Because PostgreSQL was 'hard', compared to when MySQL was younger. It just had a cli tool, it was to be managed in a more 'professional' way whereas MySQL made

Because PostgreSQL was 'hard', compared to when MySQL was younger. It just had a cli tool, it was to be managed in a more 'professional' way whereas MySQL made itself much easier to be installed and managed by even entry level and junior programmers who didn't want to know how to manage a database earlier on in its history.