I thought the same but having worked 2 years close to CIOs I have realized their job is quite hard as it is. CIOs have to navigate hundreds of technologies and each vendor wants their cut, sometimes US startups are the worst… so choosing an old established technology still makes sense for most of IT people to manage tech and vendor risks… not a great answer, I know.
I second the part about US startups. Compared to what Oracle delivers (really solid database clusters with everything enterprise customers need built in), their cost is actually not that high compared to other enterprise software. Especially SAAS that are only solve a narrow problem and can cost a lot.
To be clear, I'm all in favor to switch to Postgres for most workloads, but rather for new systems as migration old ones is either impossible or much more expensive than paying licensing fees.