And why shouldn't we judge earlier societies by modern standards?
Because they'll always fall short, and criticizing those ancient societies won't change them. You may as well save your "constructive criticism" for societies that can
All of which is a very long way of saying: We don't adhere to the meaningless rhetoric used by the Romans. We call their emperors their emperors, not their "pontifex maximus with tribunician power and imperium superseding all others."
Perhaps we shouldn't though. The Athenians called themselves a democracy, so why shouldn't we? The Roman "emperor" wasn't called an emperor, so why should we?