I think the only reason Red Hat’s model works for them is that Linux distributions are obviously massive sprawling complex things, and maintaining LTS distros which you then sell support for is an incredibly complex and valuable thing that no intermediary can plausibly claim they can do. Even if the underlying code happens to be FOSS.

Matrix servers (and web servers and mail servers etc) are not as complex - and if anything you want incentives to make them less complex, not more. And the better job you do of making them easy to admin and support (ie the more scalable and stable they are), the less reason there is to pay the upstream for support but some system integrator instead.