Monogamy is one such structure. It seems very tied to the modern idea of the "nuclear family." There are others. Having an extended family all living together is another. Tribes where children are raised communally is another.
Collectivism has clear benefits but comes at a steep price: the need to establish and enforce group norms. The nuclear family seems like a compromise in this space, a revealed preference.
I mean, I would probably be happy living like an Orca in a matrilineal family group but, then again, I've always gotten along with my Mom. What about the people who haven't? Or who only started to once they moved out? Those people would be faced with living in a disharmonious environment or leaving to a world hostile to individuals.