The idea is not to go back to the Software Engineer asking the Ops team "Hey, can you provision a Postgres database for me please?" and then waiting a week for it.
It's that the Software Engineer takes a module that was prepared by the Platform team - i.e. "terraform-postgres-mycompany" - which already includes all the requirements the company has for handling databases (think backups, monitoring, encryption, etc.). They can then proceed to use it in the small service-specific Terraform configuration, which really is just putting such ready-made modules together.
The important bit being - the Platform team isn't a bottleneck here.