I suppose a lot depends on who has the most power in a relationship and who has the greatest appeal in regards to male or female

Alternative sexual partners

It's a lot harder for the average man to get the same sexual partners as the average woman

If a man is of high quality but is wife or partner is not or that she in terms of her looks has got older and her body has gone through multiple pregnancies

The chances are strong she won't be appealing to younger man or Man her own age

From my personal life woman tend to date older men it's the social norm

And a woman at 45 years old dating a 65 years would not be what she is expecting

Open relationships have a way to opening up people standing in the sexual marketplace/relationship marketplace