Game theory offers one reasonable explanation, but a better and simpler explanation might stem from the laws of supply and demand: there are more available women than men. First, there is the biological impact (while more males are born, by age 20 or so, there are slightly fewer men than women) and then there is the judicial impact: there are many, many more men in prison than women. Even if you postulate an equal number of men and women at every level of desirability, by removing a lot of men from society by installing them in the slammer, you skew the balance in favor of the (fewer) remaining men.