That's true. The higher-ups can say which database to use and hire a bunch of people to set it up. But if the developers ignore them, they have no way of actually determining this. (Which is what's so great about mandates from Higher Up.)
I worked at a place that had a huge Oracle RAC license. We ran non-mission-critical data collection apps on it, but the app which dispensed drugs in real-time, all over the world, not only ran Postgres, but 90% of the business logic was in DB functions.
Because there are people who consider themselves technical writers. Either they do it or someone from the core postgresql team who has the credibility.
I didn't. It wasn't subversive, like the parent comment. It just worked out that way because of technology acquisitions. Customers wanted to hear their data was "on Oracle."
My take is that the overhead of maintaining and using Oracle means that you have to cut resources somewhere else. I'm pretty sure a competent DBA and developers can ensure atomicity and integrity using Postgres (instead of Oracle), and have a lot of time left over to create more features in the application.
Don't get me wrong - Postgres is awesome and I would happily use it for any project. I'm not sure Postgres is easier to manage than Oracle and places any less maintenance overhead, but YMMV.
Its just that RAC is a special technology with no equivalent on other DBs. It is usually placed where you need load balancing on the DB level. It normally has very high availability that is a good fit for mission critical DBs. I hate seeing good technology wasted, but you are right that if Postgres is already there and works well, there is no point in moving anywhere.
Sometimes, that conspiracy is what keeps the business running. Whithout it, there would be no jobs.
Not that this is the case everywhere and everytime, but if technical decisions were left solely in the hands of people that lack technical skills, the situation would be even worse that it is now, with all the "enterprise software" floating around and causing trouble directly proportional to their cost.