And I'm not sure I'd agree with their analysis, but they're clearly free to make the decision.
If larger companies can run CentOS in production, they also can run Debian or any other distro without a support contract. They could even use a competing loss leader distro like OpenSuse Leap.
Yes, they could. But they (often) don't. The certification / training ecosystem that exists around RHEL has a lot value, even if a lot of folks like to handwave it away. The engineering that goes into RHEL and the very predictable lifecycle has a lot of value, too. I'm not going to say that Debian or SUSE aren't equally good, engineering-wise, but it seems like a lot of large companies have chosen RHEL clones over Debian. (Not all! I am sure plenty of companies do as you suggest with Debian.)
Don't get me wrong - I think it'd be great if Debian became the standard, assuming that meant that companies helped develop Debian and poured resources into it as a commons. That'd be much better than depending on Red Hat to do all the work and then not paying for it.
Lots of companies do contribute to Debian and this has been happening for a long time. To start with Canonical employs people to contribute back. For a while HPE was donating large amounts of server hardware. Several companies (early HP, ARM etc) contributed lots of work on new ports like arm64, hppa, etc. Almost the entirety of the LTS effort is funded by companies. The current status is summarised on on the wiki:
Many companies just needed some linux. So, choosing between Debian and Centos was pretty much choosing between rpm and apt. Many companies were not choosing between the commercial RHEL and Centos to begin with.
Now they are just fine with just containers.
It used to be for standardization, but I've seen more commercial tools provide Debian / Ubuntu support than Red Hat lately, since the late 2010s. I also think the amount of changes and the issues with licensing here mean that more people might up and convert to Debian than before. But IDK. I also hear that more ML work is done on Debian, and yes - with the containers becoming big - less need to run any particular linux, so I could see swapping out the underlying Linux.
And from a company perspective, Red Hat has already done a big swap out from satallite to Foreman / Puppet to really pushing Ansible. Similarly, they've stopped doing oVirt in favor of cloud style OpenStack, nee OpenShift. Which is great if you're building your own cloud fabric, but not really the VMWare / HyperV competitor oVirt was which is something lots of mid size orgs need. ProxMox still seems to be going.
And for people who aren't paying for support - I imagine they have skilled in house teams that can certainly figure out Debian if they've been orchestrating CENTOS and now Alma say.
If larger companies can run CentOS in production, they also can run Debian or any other distro without a support contract. They could even use a competing loss leader distro like OpenSuse Leap.