Sperm competition too. Sometimes you do not have to be the toughest, just leave about the mostest. Kinda like jack salmon or sneaker bluegill, or the teenage kid you think just mows your lawn.Probably because of the group breeding that hatcheries set up. Seem like only the most aggressive would end up actually breeding the hens while running off the lesser more docile roosters. Not exactly a trait that's desired in layers. The cheapest way to get numbers of chicks though.