First, Oracle has completely open sourced the JDK, for the first time ever. Instead of a JDK with a complex license, mixing both free and commercial features and containing field-of-use restrictions, Oracle now provides the JDK under a 100% free and open source license, or under a commercial license for those who wish to purchase a support subscription (and fund the development of OpenJDK).
Second, there are no longer major releases, and the new feature releases are similar to the old six-monthly "limited update". JDK 10, 11 and 12 are roughly the same size as 7u2 and 7u4, which also didn't get free security patches after six months. What's changed is the name given to those releases, and to make the updates cheaper and easier, they have been made more gradual, by allowing spec changes in feature releases. Not only do you get security fixes for free forever, but there are no more major upgrades.
So the main point of confusion is that some confuse the new feature releases with the old major releases, when, in fact, they are much closer to the old "limited update" releases. People see a new version number, see that that number is not freely supported beyond six months and panic, when, in fact, the old releases that were similar to the new feature releases were also not supported beyond six months. They themselves were considered "updates" to some major release, but major releases no longer exist, and the "updates" now get a new version number. See here [1] for a more complete explanation.
In addition, there's another new model, that allows organizations that for some reason need a much less gradual upgrade process than the new one -- and even less gradual than the old one -- and that is something that Oracle charges for. But because the JDK is now completely open source, other OpenJDK members have committed to backporting the fixes to provided a similar step-wise upgrade path for free.
(I work on OpenJDK at Oracle, but speak only for myself)
[1]: https://www.reddit.com/r/java/comments/bav1sy/winter_is_comi...