> Maybe I'm not the target market for this, but how hard is it REALLY to manage a RDBMS?

It depends:

- do you want multi region presence

- do you want snapshot backups

- do you want automated replication

- do you want transparent failover

- do you want load balancing of queries

- do you want online schema migrations with millisecond lock time

- do you want easy reverts in time

- do you want minor versions automatically managed

- do you want the auth integrated with a different existing system

- do you want...

There's a lot that hosted services with extra features can give you. You can do everything on the list yourself of course, but it will take time and unless you already have experience, every point can introduce some failure you're not aware of.