Trying to answer it objectively:
In many applications, what drives your choice of distro is ultimately the software you are going to run there: you don't want to run your business-critical applications on a distro with a short life cycle, where you will have to upgrade to a new version every 1 or 2 years or lose all updates. Nor you want to lose money because a very important application does not work well with your chosen distro or breaks after an update.
Many of those applications (e.g. a list from Red Hat lists lots of certified software) are certified for RHEL (and sometimes other distros): you can run them in any other distro, but you're on your own if something wrong happens, an update to your distro breaks something, etc...
From personal experience: at university I used some CAD software which was certified to run on RHEL. We ran it on CentOS boxes, but I got it working on Arch Linux with some work - I didn't mind doing it, but in an application where this app was critical, it would be unacceptable.
RHEL (and thus CentOS, which is based upon Red Hat's sources) provides this with a 13-year-long support cycle (however, at a point you will only get security fixes - no new hardware support). For Red Hat, this support is backed with legal contracts - which matters in a business situation where one needs official (sometimes urgent) support to be fully accountable.
Debian has a shorter life cycle (4 years) and is community-driven: while you usually can get good help from the community, and the community does lots of testing, you will not be able to get a support contract, you don't have official support, etc... And it's harder for them to certify hardware.