Most web hosting providers use CentOS and many of them use CloudLinux. For those using cPanel on CentOS, this will be a logical choice especially if they're already using CloudLinux (many are). Plus they plan it possible to convert CentOS 8 to their new RHEL fork, which perhaps Rocky Linux plans on doing too.

Given the installation base of cPanel, whichever fork they decide to officially support will probably win out. And I'll be dollars to donuts that they'll pick CloudLinux's fork, since they already support CloudLinux.