There are others but they’re not as significant as the cheese reserve once was.

Part of that is cost of administration. Cheese was developed to store dairy many thousands of years ago. It’s inherently relatively stable so to store it all you need is a cave and a soldier to man the entrance. Grain has a shelf life and needs to be periodically rotated and inspected to keep mold and bacteria from spreading, so you need that soldier and a bunch of people who know how to prevent bulk loss.