I hadn't thought of that, but yes that would be another very possible mechanism.Another thing to consider, is that some animals have a population mechanism to control population when pressure gets too high. Since most chickens live in extremely cramped (if safe) environments, if they have this kind of mechanism it would likely be triggered in a coop situation.
That would be another thing that is stronger in some chickens than others, because of how common it is for a given flock to include some hens that go broody regularly and other hens that never go broody even when they all live in the same conditions.