It appears they have different requirements for those machines. They state the Ubuntu machines are for non-firewall applications. Ubuntu and Debian can configured relatively easily for a number of workstation and server roles.

Also many IT professionals that have used Linux will be familiar with a Debian or a Debian derivative such as Ubuntu. That simply isn't the case with OpenBSD.

I recently installed OpenBSD on my old laptop to try it out and I found it difficult even though I used to use it at University back in the late 2000s.