Earlier quoted context omitted.
Arguably, no one should be running a server that long in 2020. I would say a better reason is that while both are Linux distributions, they are distinct dialects and ecosystems. It isn't impossible to switch, but for institutions that have complex infrastructure built around the RHEL world, it is a lot of work to convert.
It's not really about running servers for 10 years. It's about having a platform to build a product on that you can support for 10 years. RHEL software gets old over time, but it's still maintained and compatible with what you started on. Consider an appliance that will be shipped to a literal cave for some mining operation. Do you want to build that on something that you would have to keep refreshing every year, so…
This.
A decade ago I was technical co-founder of a company [0] that made interactive photo booths and I chose CentOS for the OS.
There are some out in the wild still working and powered on 24/7 and not a peep from any of them.
We only ever did a few manual updates early on - after determining that the spotty, expensive cellular wasn't worth wasting on non-security updates - so most of them are running whatever version was out ten years ago.
Rock solid.
[0] https://sooh.com