Perhaps it's simple economics at work, with a physical foundation - men make many low risk investments whereas women make a handful of extremely high risk ones (bearing a child is physically very costly). Thus, men will be more inclined to approach and, therefore, lower their market value by increasing supply, while women will be more inclined to shoot down offers, since they are in great demand. I think that the society you're talking about would either have to be one where men have mutated into childbearing creatures or one where women have mutated to have very short and early pregnancies. An alternative might be a society where men take the brunt of the work of raising kids, though this is unlikely because women are more socially inclined due to their neurochemistry and, therefore, better at providing the emotional support a child needs, not to mention that they need to breast feed and physically recover after delivery which makes them less able to actively find food and shelter.