There is no irony other than the fact that you think it's ironic. Monogamy is the default for same-sex couples as well. Orthogonal issue.
The issue with non-monogamy is that a pairing (2 people) is the smallest working group, and that's what the game theory of dating proves to be most durable and successful. A 3-person working group requires at least 3x more relationship work, and a 4-person pairing requires 6x as much.
The issue with non-monogamy is that a pairing (2 people) is the smallest working group, and that's what the game theory of dating proves to be most durable and successful. A 3-person working group requires at least 3x more relationship work, and a 4-person pairing requires 6x as much.