Thought experiment: why doesn't the United States have something like 20 years worth of calories for every American stockpiled by now? I'm more than half-serio

Thought experiment: why doesn't the United States have something like 20 years worth of calories for every American stockpiled by now? I'm more than half-serious. Skim a few percent surplus of stable oils and dried peas over the years, build up a reserve, stick them in vaults in Montana and Virginia. The cost would be quite small, even trivial, in the grand scheme of things. What if there's a volcanic eruption and we spend half a decade in semi-darkness? Our civilization probably could survive that if we prepared. And we know something of that scale happens every few thousand years. We have more potential for reserve capacity than ever and yet we run on razor-thin margins even for the basics of life.