I suppose, in evolutionary terms, it's the same as any group of excess males -.they just keep challenging for the top place, and the sex, and the responsibilities that come with it, and the strongest and fittest get the girls for as long as they're able to hang on to them. Maybe if they spend a lot of their time showing off to each other in a noisy way, they act as lures for predators and thus reduce the risk for the quieter, more valuable hens . But we poultry keepers try to organise things for them so they can't fight, our neighbours don't like all the noise of one cockerel, let alone a bunch of them competing for the loudest crow, and we don't usually want to feed unproductive birds.