This presumes the game is entirely a competition to see who gets more sex. Poly and open relationships can have other advantages. For instance, a lot of men are

This presumes the game is entirely a competition to see who gets more sex. Poly and open relationships can have other advantages. For instance, a lot of men are effectively in a second relationship with their work, which often destroys monogamous relationships due to loneliness on the part of the ignored partner. Divorced parents often have a special relationship with their children, with a connection that is fed by lots of alone time with their kids. Poly relationships also open up effectively a new kind of family dynamic, in which metamours have a deep relationship that may not be sexual but allow a lot of trust and reliance. Finally, even if it really were about who gets more sex, men become much more attractive relative to women in middle age. The silver fox effect is real... sex is also a lot easier for men with lots of social status, which can also come with age.