I think that the implication is that if each individual hunts individually, they mostly get nothing, and every so often get an entire animal which is too large

I think that the implication is that if each individual hunts individually, they mostly get nothing, and every so often get an entire animal which is too large for one person/family to eat, so the expected value of this strategy is low. By pooling high risk strategies with big payoffs, the expected value of the whole is greater.