Your headline's misleading. Red Hat knows it's long been fixed in the LTS kernels, but it still needs patching in the RHEL kernels. Generally speaking, current LTS kernels are not used in older Linux distros.
'current LTS kernels are not used in older Linux distros' - not sure what your point is with this. They absolutely could have used / can use LTS kernels if they wanted to or they could merge LTS-kernel changes which they apparently don't.
https://bugzilla.redhat.com/show_bug.cgi?id=1708775
I don't see what the big news here is, it's merely identifying a vulnerability with a proper CVE ID, end of story. The issue itself does not even have a serious security impact so it will likely never be fixed in RHEL.
Debian always uses longterm branches. Sometimes Ubuntu, too.