[nerdjon]

Do we actually know this for certain? We have a very curated view of many past civilizations and in many (most?) cases it is a very heteronormative view.

I have seen plenty of arguments that monogamy did not become "normal" until religion entered the picture and the idea of woman as property became a thing (ironically the fact that some religions reinforce this by a man having multiple wives).

There is absolutely no reason to believe monody and civilization matters in the slightest. At best you could argue (and I would agree) years ago needing to be concerned about a woman getting pregnant, but that does not hold any weight in a modern society.