OSX user management is weird. At least on prev versions, they don't show a root account in the Users & Groups ui. A guess: there's a code path in the UI that

OSX user management is weird. At least on prev versions, they don't show a root account in the Users & Groups ui. A guess: there's a code path in the UI that is only tested on "mac" accounts, not the root account that the system requires to exist. Something about the non-macness of the root account interacts badly with the UI that expects to be run on a mac users account.