> AlmaLinux and RHEL remain the main supported Linux distributions across much of the organization
Alma and Rocky provide almost the same thing.
I suspect that at the time they had to make a decision, Rocky Linux was not in good enough state, so they went with Debian, and now they already standardized around Debian, so no need to change.
Debian is to be used for some legacy systems because RHEL introduced microarchitecture restrictions. Rest of their infra is on AlmaLinux (a RHEL-compatible distro ala Rocky).
CentOS was always the hosting companies OS, which is continued with Alma Linux. Rocky certainly not