Until Red Hat starts to add backports or fixes for customers that don't get push back upstream. Then when X+1 gets to RHEL it's missing all the previous RHEL only updates (some not backport related).
Is there a world in which the vast majority of dev work isn't brutally monotonous? Most work's writing unremarkable code for unremarkable products containing unremarkable features that have already been implemented 1,000 times before, and likely even more than once before for the person doing the work. A ton of dev time, at least for people who aren't the much-derided solo-language-experts (e.g. The C# + Windows programmer, the Java programmer, who only do those kinds of jobs and don't even dabble in much else) is just wrangling the unfamiliar-brokenness of a tool & library ecosystem (it would be familiar-brokenness 5 years in and take up little of your time, for most non-trendy platforms, but you're either using a trendy one that changes way too much, or will be on a different language + ecosystem entirely before you hit 5 years on this one).
Very little dev effort is working on anything cool, and very little of the code for cool projects isn't kinda boring and normal.
RHEL 7 came out 6 years ago with Linux 3.10 and is still getting patched. Somebody has to manage and integrate all those security fixes in all those packages without breaking the old codebases.
Ksplice (Oracle) was first, followed by kgraft (Suse), and kpatch (RedHat).
According to the article below, kpatch is x86/64 only, uses ftrace, provides runtime patches only until the next minor kernel release on a standard license, does not address all CVEs, and cannot be used with "SystemTop or kprobe."
Actually, POWER9 RHEL7 has Linux 4.x, where x depends on the minor release -- unfortunately not the latest on the system I use. I think aarch64 is similar, but I'd have to look for rpm to check. They need similar attention, of course.
Anyway, RHEL kernels have various features backported to the vanilla version on which it was originally based, not just security patches, which probably makes the job harder. It is a major effort.
Maybe they're reading this comment right now, hi!