RHEL 7, and in turn, CentOS 7, were supported until June 30, 2024.
CentOS Stream 8 builds were supported until May 31, 2024.
CentOS Stream 9 is the latest official stream for CentOS, however it is a moving target that is not suitable for production use.
Rocky Linux "is an open-source enterprise operating system designed to be 100% bug-for-bug compatible with Red Hat Enterprise Linux" according to the web site.
The packages and tests for this application use Docker exclusively as that is the best method for a portable and repeatable build and test process. As such, it is necessary to use official images when building for the various platforms. With Ubuntu and Rocky Linux this is very easy as Docker Hub contains official images for all releases. However, for CentOS and RHEL this becomes much more difficult.
The old CentOS docker images are deprecated and are no longer maintained. The package repositories for CentOS 8 are broken or gone entirely, so building for that release would require using a hacked up, manually built, base image.
The docker images for the latest "stream" builds for CentOS, stream9, are only
available on a RedHat site named quay.io, which requires a
RedHat account to access.
For these reasons, the packages for RHEL 8 and 9 are built using the Rocky Linux 8 and 9 docker images.