I don't even know how Oracle is still the juggernaut that they are. A $10,000 dollar computer running postgres can serve a ridiculous amount of queries. I suspect the general idea is to spend huge amount of money to run incredibly inefficient SQL queries.
1. Oracle does provide value. They have clustering and high-availability offerings that Postgres just can't touch, and those come with service and support personnel as part of the contract. A one-stop solution is a powerful sales pitch.
2. They have a massive existing install base within the Fortune 500, which spend amounts of money that the average hacker just can't grasp. Somebody that I know very recently worked on an enterprise project to create more-or-less a web page that had a $1,000,000 budget. Oracle is not asking for unreasonable amounts of money, by enterprise standards.
3. Companies value safety over risk, and Oracle has a long track record at the executive level of providing safety. The mindset goes something like: Postgres might be good enough for Imgur or Joe Bob's Bait Shack And Social Network, but neither of those is a bank, healthcare provider, or an entity capable of ordering an air strike. Oracle is telling the story their customers want to hear.
4. Because Oracle has such a large install base and so many success stories at the enterprise level, they are one of a very few number of default choices that an enterprise will make. They have spent decades building up sales momentum.
Business decisions usually have very little do to with the underlaying technology.