Disclaimer: I'm very involved in the kernel part of this for $company.
The RHEL kernels themselves do see many improvements over time, the code that you'll see when the product goes end of life is considerably updated compared to the original version string that you see in the package name / uname -a. There are customer and partner feature requests, cve fixes and general bug fixes that go in almost every day.
The first problem of 'running old kernels' is exacerbated by the kernel version string not matching code reality.
The second probelm is many companies don't start moving to newer rhels when its out, they often stick to current -1, which is a bit of a problem because by the time they roll out a release, n-1 is likely entering its first stage of "maintenance" so fixes are more difficult to include. If you can think of a solution to this, I'm all ears.
The original reason behind not continually shipping newer kernel versions is to ensure stability by providing a stable whitelisted kABI that third party vendors can build on top of. This is not something that upstream and many OS vendors support, but with the "promise" of not breaking kabi, updates should happen smoothly without third party needing to update their drivers.
The kabi maintenance happens behind the scenes while ensuring that CVE fixes and new features are delivered during the relevant stage of the product lifecycle.
The kernel version is usually very close to the previous release, in the case of rhel10 its 6.13 and already with zero day fixes it has parts of newer code backported, tested, etc in the first errata release.
The security landscape is changing, maybe sometime Red Hat Business Unit may wake up and decide to ship a rolling better tested kernel (Red Hat DOES have an internal/tested https://cki-project.gitlab.io/kernel-ark/ which is functionally this ). Shipping this has the downside is that the third party vendors would not have the same KABI stability guarantees that RHEL currently provides, muddy the waters of rhels value and confuse people on which kernel they should be running.
I believe there are two customer types, ones who would love to see this, and get the newest features for their full lifecycle, and ones who would hate it, because the churn and change would be too much introducing risk and problems for them down the line.
Its hard, and likely impossible to keep everyone happy.