They explain it as these holes are at the top of the mountain. Why climb the large mountain to store your grain there just to have haul it back down later? My own guess answers: safer from animals, precipitation, safe from enemies.
Storing in general could mean different things: putting baskets with grain and produce there for a minute and them someone else immediately pick it up in some bartering exchange, it's not really storing then, I guess? Or, even religious offerings can also be explained as "storing" -- they are stored in there until the "gods" (i.e. elements) destroy them (i.e. consume them) and the gods are appeased, that way ensuring good harvests and other benefits.