Males are much more of the sexual agressor of the species.

Same thing happens in many other species... lions for example. If the young guy comes in and bangs all the women, he gets to be alpha male. If the already alpha male gets busy with all the women, he's just taking advantage of the fact that he's in a higher posisition and he's looked down upon by the other males. It's not odd, it's reproduction and the procreation of the younger stronger male.