Oracle contributes about 90% of development (80% of the issues, and almost all new JEPs). Red Hat contributes ~5%, and IBM only 1%. So the recent Red Hat acquisition improves their position a lot, but before that Oracle and IBM paid for the majority of OpenJDK salaries the same way Bill Gates and I combined have billions of dollars.
* https://blogs.oracle.com/java-platform-group/building-jdk-11...
* https://youtu.be/wHoRBvt3U6o?t=830