kutaḥ ---, narāṇāṃ sāmarthyabhedāt vāyoḥ śrotrasaṃskārasya sannidhānāsannidhānābhyāṃ śrotrasaṃskārasya bhinnatvāt sāmarthyabhedaḥ //
Why? Because of the difference in men's capacities; this difference in capacity exists due to the presence or absence of air that embellishes the auditory organ.