Because it involved a full backup - which wasn't anywhere fast on Proxmox, reinstalling the host, a full restore and then tinkering with the famous "runs everywhere (and not Java!)" boot shenaningans of that flavour of Linux OS.
And that was with the help of a backup-recovery solution which did support Proxmox, mere 6 months before that I would had stuck with an agent P2V migration of a VM to VM - which would had involved way more moving parts (can't P2V/V2V to a hypervisor which is not even installed yet) and more pain.
And that was with the help of a backup-recovery solution which did support Proxmox, mere 6 months before that I would had stuck with an agent P2V migration of a VM to VM - which would had involved way more moving parts (can't P2V/V2V to a hypervisor which is not even installed yet) and more pain.