They do have a robust testing process, but their main focus at the CentOS Stream stage is more about preparing for the stable RHEL build than it is about adding a ton of new features and bug fixes. Testing takes time so it would be physically impossible for them to test everything if they didn’t have a limit on the type of contributions they accept. For bug fixes, their limit is that the bug has to be critical. For bugs lesser than that, the correct place to contribute those fixes is in Fedora.
That has been adequately explained in the merge request at this point, if you click in that link at the top of this thread amd read through it to get the latest info. The Red Hat devs have also made no indication that they’re not welcome to contributors. Anyone who’s saying that is blowing this merge request issue out of proportion.