There's an enormous amount of larger businesses for whom the database _is_ the business. (Well, databases plural, they'll inevitably have many.)
I've worked for places where the vendor of the software that sits on top of the DB is either defunct, gone AWOL or too pricey to consider upgrading what ever version of software we were using.
I worked one place where we had to large hadron collide data from Sybase and Oracle together. Live. No batching. The whole thing had to plug into some decades old Delphi crud apps + some financial software somewhere else.
Oracle + dblink made that possible. It even, as I recall, did proper two-phase across the dblink. I merely queried -- yes, I know PG kinda has the same feature nowadays -- across the database boundaries and wrote some pg/Sql to make things work. 10 minutes and $10k (or w/e the Sybase connector cost) later and we had a POC, and later that month, a working system.
Pretty? No. But it worked well, and two disparate software products written in different eras that were never meant to talk to one another now did. And it saves us millions in licencing + bespoke software and expensive consultants.
There are few limits to what you can do with Oracle, and that is its strength. When you have weirdo requirements, you can probably do it with Oracle + some skilled DBAs and be assured it'll still run in 20 years.
As for PG: I love PG, and use it for everything greenfield. But its replication is still a planet-sized joke. There are more competing methods and processes than there are JS frameworks. With Oracle, you've got DBAs who know this stuff inside out, and it works, and it has a million-billion ways of matching the needs of your business. With PG? I don't even know who to call if things are up the creek.