It's interesting to see this in play at different companies. Some of it is "real"...that is those requirements really do apply. In many places, though, it's just inertia. Like, back when the companies had SunOS or HPUX, they made internal standards about regulations, or support contracts, etc, to match. Then when Linux came around, RedHat fit their view of the world well.

It's also interesting to see what happens there in some places over time. The older group that manages on-prem is able to hold the "RedHat only" line. But, other groups decide what goes on it, so everything running there is running in non-Redhat containers or nested VMs. It turns into a bulky, extra hypervisor-like layer.