Why do you think being pregnant has anything to do with who pursues who?

You described an alternate scenario, but I still can't seem to connect the dots. What does pregnancy have to do with pursuit? What does frequency of insemination have to do with pursuit? Why isn't society structured in such a way that women are in charge and use men as semen providers and nothing else? That would also be a completely viable societal structure that fits within the biology. So why not that?