"Doesn't cost anything": This is a meme that is largely false.
Any large organization will buy support for open source software which can sometimes be actually more than the cost of a database license (see Datastax and Cassandra).
License, support, take your pick. It takes people to keep systems running.
We're moving from Oracle to Postgres. From three huge Oracle instances to, pretty much, a cloud of Postgres boxes, a pair per application. Because we can.
Oracle is a superlative database, but it's the polar opposite of agile. This turns out to be important.
Any large organization will buy support for open source software which can sometimes be actually more than the cost of a database license (see Datastax and Cassandra).
License, support, take your pick. It takes people to keep systems running.