They already did that. The previous release was based on Android 6, and is functionally useless nowadays given that it only runs on a couple of Samsung devices all released around 2011-12.
If you're trying to maintain a fork of a large open-source project, and especially one which needs to interoperate with external systems like Android, keeping up with upstream releases is not optional. The upstream will move on without you.
If you're trying to maintain a fork of a large open-source project, and especially one which needs to interoperate with external systems like Android, keeping up with upstream releases is not optional. The upstream will move on without you.