[rurban]

Because debian and ubuntu are not trustworthy enough as server platform. They are not involved in the technical details of the basics, such as compilers, binutils, libc, kernel, systemd, gnome, wayland, servers, ... contrary to RedHat and Suse, who are maintaining these things. CentOS is the server standard. Which was the free RHEL variant, without support. 80% of the world runs this.

Debian and Ubuntu also have a horrible security track record. For devs behind a firewall it does not much harm, and they try to attract much more packagers with their focus on petty law and social issues. Which is fine. Most prefer the political issues, but some prefer the technical competence.

[jgowdy]

I think you'll find in the modern era / younger generation, running Ubuntu on the server is actually very common. Especially in the cloud. Most usage of CentOS I've seen in newer builds is strictly for hardware that requires vendor driver support, which is becoming more and more rare as vendors upstream their drivers.

CentOS was the server standard 10 years ago. And most of the downstream distros like Scientific Linux and Oracle Linux are dying.

80% of the world runs this, citation needed because I don't think that's remotely accurate and likely represents your personal bubble.

https://distrowatch.com/

[jgowdy]

Besides, on the server the real trend I've seen is Alpine. Far less attack surface than CentOS anyway. If your applications work with musl libc, you're in business, and worst case you can install glibc (which packages like OpenJDK do).