It's still "respectable" to run your own n=1 Postgres instance, maybe with WAL-E backup. It's sensible, as well, to create your own read-replicas to scale OLAP; and even to do your own shared-nothing sharding across regions. These are all "set and forget" enough that they can be the responsibility of your regular devops.
But, when you get to the point where you need multi-master replication, you're making a mistake if you aren't dedicating an ops person (i.e. a DBA) to managing your growing cluster. If you can't afford that ops person, much better to just pay a DBaaS provider to handle the ops for you, than to get hosed when your cluster falls apart and your week gets shot putting it back together.
But, when you get to the point where you need multi-master replication, you're making a mistake if you aren't dedicating an ops person (i.e. a DBA) to managing your growing cluster. If you can't afford that ops person, much better to just pay a DBaaS provider to handle the ops for you, than to get hosed when your cluster falls apart and your week gets shot putting it back together.