They won't say it, but the reason for this is 100% to kill downstream distros based on RHEL. They already effectively killed CentOS, the downstream distro they controlled, by moving it from downstream to upstream. With this change they're now coming for other downstream distros that they don't control, like Rocky Linux or AlmaLinux. Upstream repos like Fedora (and CentOS once it changed to CentOS Stream) will not be affected... for now at least.
I think downstream repos are important to the ecosystem because they give the FOSS community contributors an easy way to test against RHEL-compatible binaries without being encumbered by an RHEL license. IBM seems pretty hellbent on ensuring that people won't be able to do this without agreeing with their license, and as soon as they achieve that I think they'll tighten the screws on their own licensing in ways that aren't to the benefit of anyone but IBM. It seems pretty obvious to me that IBM is making this change because they see some advantage in having absolute control of the licensing terms, and my guess is that their benefit will come at the community's expense. Yes, you can get a free (as in beer) developer account and test using that but now you have to register VMs, keep track of your number of registered systems, and you have to worry about possibly violating the not free (as in freedom) license that you have to agree to in order to access the Red Hat developer program. I think this change will be bad for RHEL in the long term, but time will tell.