Point is, if you work for some big corp, when you buy something, you want proper warranties meaning people to blame if it breaks down. I have seen corps want to pay for stuff available free just so they can point at someone if there's a problem. Ubuntu is mostly fine, Canonical does offer support, but "nobody ever got fired for choosing IBM".
The enterprise support also means security updates, which is a huge requirement for government contract work (not just US, anything military really). I've also seen requirements for use of DISA approved products. I think at the time RHEL and maybe SUSE were the only ones on the list - I'm a few years removed from having to care about this.
Professional applications (e.g. CAD,...) generally don't support many distributions. In my field, RHEL and SLES are widely supported and a few tools also support Ubuntu.
We've got over two hundred Rocky/Centos vms. all of them 'pets' that would require manual migration of lots of very different services, many of them bespoke. That's quite a lot of work.