I'm sure this is mostly due to the economy but I would be interested to find out how much of this is due to lack of funding after the CentOS Stream thing.
I know people love the idea that CentOS was somehow bringing business to Red Hat and/or the change to CentOS Stream caused Red Hat to lose revenue but ... not so much.
If people moved from CentOS to Rocky or Alma, they weren't likely to hand money to Red Hat in any event. I have no idea whether or how many people were converted from CentOS 8 to RHEL, but I doubt that was a huge bump either.
(Full disclosure: Former Red Hatter, no longer there as of last year. Not directly or even peripherally involved in CentOS for a lot longer than that.)