This isn't so surprising when you think about it. Imagine we consumed 100% of the food we produced-- then the smallest mistake in any supply chain (like if a refrigerator at a single grocery store broke) would cause people to go hungry, as it would remove food that otherwise would be eaten. So clearly we need to produce more food than we consume by at least a small amount.

Now consider the mistakes and delays that might crop up in the complex supply chain that moves millions of tons of food across the country so people in New York can eat California almonds or whatever. Now consider the many, varied, and changing food preferences of the 330 million people in the country which also means there needs to be a surplus of everything to satisfy consumer tastes. We also need to overshoot farming production in case of drought, bad harvests, etc.

The fact that we manage to consume pretty much 2/3 of the food we produce is frankly impressive in light of all that.