My understanding is that CentOS as we once knew it (the freely-distributable rebuild of EL 7 and earlier) withered away because its creator and primary maintainer was hired by Red Hat. There was a clear conflict of interest at that point, and Red Hat probably wasn't going to keep paying him to maintain a project in perpetuity that ate into their bottom line.

https://www.linuxfoundation.org/blog/centos-project-leader-k...

So it's not so much that RHEL tried to strong-arm third-party rebuilders of Enterprise Linux - and I don't think it's in their culture to try - but people involved in these projects are always at risk of being bought out. Volunteering for open source can be a lot of work.