> Kind of like how RHEL used to still provide contributions to CentOS for a long time (although I think that ended at some point too).

RHEL contributes to CentOS now more than ever.

CentOS started outside of Red Hat (2003), and didn't get any direct contributions from Red Hat. It built from RHEL sources, which is an indirect contribution that didn't involve any Red Hat employees. Later Red Hat hired most of the CentOS maintainers (2014), and contributed to CentOS by paying their salaries and providing hardware resources, but that was where the contributions ended. This was the status quo until 2021, which is when RHEL maintainers were onboarded to CentOS, drastically increasing the number of people working on CentOS.