The question is what level of maintenance is required to call something "supported." But yes, there is some maintenance done for free on old versions of the JDK in OpenJDK Updates in the form of backports.
The thing is that the money saved in hardware/hosting by running the current version would more than pay for any update costs. By using the current version, companies will be using better maintained software and paying less money for it. Those "free LTS" builds, which aren't really LTS, is a mind game that keeps companies on old versions that cost more money to run in the hopes that people will ultimately pay for real maintenance, perhaps once they fall behind too far.
