There is a difference between package documentation and system documentation. Red Hat contributes package documentation upstream, but system documentation is by its nature distro-dependent.

Red Hat has contributed work that made distros more homogeneous (cough systemd cough) and excellent package documentation for that work; but also got flak for that...

They also have soooo many good articles (which are helpful not just to RHEL) behind a subscription wall. If you do a lot of work in the rpm ecosystem, they're like the Experts Exchange of Google search, with how many times you see an exact bug report, then you get to the page with a tease of your exact answer, but it fades into the login required bit.

If you download the Red Hat developer edition and run a "yum update" once every couple of months, then you will get access.

The developer edition is now more inconvenient, as you have to reapply once a year.

And it used to be open, until Oracle started closing their tickets for paid support with essentially cut-and-paste of access.redhat.com. That's why you can't have nice things.