<sigh> This is not an answer. Merely a restating of the problem. I want thoughts about WHY this is so. What's the reason/advantage (assuming there is one) for only one.

e.g. In the past, women have traditionally stayed home w/the children while the male went out & provided financially for the family. Some might argue this left the woman in a potentially vulnerable position if her male were to leave. Given that many women today are financially independent, one could argue this is no longer a valid reason for the woman to want exclusivity/monogamy. Again, just for example.

???