Because that's what we did last time

It's difficult to think of a better example of cognitive inertia than the milk and bread rush:

This mass accumulation of dairy and dough has become an American snowstorm tradition. The only problem: Milk and bread are pretty bad survival foods. That milk will die fast if your refrigerator loses power, and bread can only offer so much nutrition during its short expiration date.

That which does not kill us makes us do that again.