Which they do get the air from the disturbance. How do you think there is air in water run through a canister? Disturbance. Is simple science. The more surface area the more contact to exchange air. Same thing with plants. The bigger the leave the more photosynthesis can occur which in turn allows growth.
Yet, it requires more sugars and nitrogen to grow as it gets larger, and thus, slows down it's growth. Well, in most plants it does...