[jbmsf]

I think it's economy of scale, not kool-aid.

I can run PostgreSQL myself but there's a ton that goes into running it with redundancy, backup, encryption, etc that takes deep expertise to well. I know from experience that it's easy to get database failover wrong. I could probably cobble something together, but it would be mediocre and wouldn't handle network partitions reliably. On the other hand, RDS is used at a scale well beyond what I could afford to build out and has benefitted from much more usage. Problems that are low probability for me are regular events for RDS and have that experience built in.

Ultimately, you are paying a cloud vendor for service value and operational experience. Some services aren't as good as others in both regards, but for the ones that are good, the overhead of doing it yourself is an exponent, not a fraction.

[zmmmmm]

To be honest, I would probably fit RDS more into the infrastructure layer than the application layer. I think there is value in having things at that level be managed.