There's actually a bespoke object metamodel mapping atop the RDBMS, and it permits customers who want to use SQL direct to the database to do so.

And, IMHO, PostgreSQL is the default choice for most storage backend purposes, unless one has figured out a good reason something else is better. :)

There were also multiple kinds of large blob storage needs, and changing architecture needs over time (e.g., multi-tenant, changing authn implications of things like browser plugins, scalability, move to cloud), so systems programming skills and controlling your framework comes in handy, for not getting stuck or blocking on vendors, but just solving the problem.