A superficially modest blog post from a senior Hatter announces that going forward, the company will only publish the source code of its CentOS Stream product to the world. In other words, only paying customers will be able to obtain the source code to Red Hat Enterprise Linux… And under the terms of their contracts with the Hat, that means that they can’t publish it.
The problem here is not the source of the applications, but the source of the package build scripts - which in big parts are RedHat property.
RedHat must provide you the sources - but for that it is sufficient to give you the source of whatever is packaged. In the past commercial distributions just fulfilled that requirement by dumping source packages, which have the source as well as the scripts required to build binary packages. They do not have to provide you with the build scripts.
The problem with RedHat is that many companies certify their stuff to work on RedHat - so for that to work without running into the occasional obscure problem you need to build the sources the exact same way as RedHat is doing. That’s what CentOS used to do until version 7, and that’s what currently some other distributions are doing. Without the build scripts it’ll be next to impossible to do that - you’d pretty much have to duplicate the RedHat engineering team. But it is completely legal, as they own the scripts, and since they’re completely separate from the application itself don’t have to be GPL.