There's a self-fulfilling cycle that happens here in both history and anthropology where the assumption when looking at old cultures has been that they were a patriarchy, because that's all we've ever seen, because every time we look at an old culture we're assuming it's a patriarchy, so when we see things that look like a matriarchy we assume we're mistaken because everything else we've seen has been a patriarchy, so this must be one, too.

For instance, looking at the art from Minoan Crete, there's abundant examples of works where women are portrayed in the ways that in other cultures of the region were how the rulers were portrayed, but since we're assuming they were a patriarchy, the assumption has been that these were gods being portrayed, and not rulers, because rulers are men and these were women, so they couldn't have been rulers.

You see similar where we'll find grave sites where the skeleton seems female, but they're buried with the trappings and in the fashion of a ruler, and a shocking amount of effort is spent trying to reconcile that contradiction.

(This is not to argue that Rome was actually a matriarchy or anything silly like that, rather that the blindness of history to the role of women reaches almost comical levels in other places, so it's not surprising to find a blank spot in Roman history in pop culture, at least.)