This is it. I used to work for a consultancy that specialised in Oracle products. Turns out if you want an ERP or HCM, running Oracle EBS with a DB backend on Oracle...running on Oracle Linux...on Oracle Linux KVM hypervisors (where CPU pinning is a recognised and allowed tactic - unlike Oracle on other hypervisors)...it turns out, might be competitively priced.

It's a total lock in. Also, I get the impression that it's almost always up to what the Finance team is used to/familiar with. They decide the finance app - then everything else follows as above due to the financials...which they are in charge of.

I know a guy who migrated workloads off PostgreSQL Enterprise back to Oracle as the performance and availability just wasn't good enough. I don't know enough about DBs to query that much, but he did it.