Food is sold on the open market, much like oil. As the adage goes, the first world pays more, and the third world starves.
But market aside, a lot of our food independence is rather... inefficient. A excessive amount of crops we grow aren't for eating, at least by us. It goes to feed livestock. Be it for milk, eggs, or to be slaughtered for meat. Extremely inefficient in terms of cost and water usage, which is just the kind of thing we need while dealing with a drought.
And the last big thing, we aren't exactly fans of seasonal diets. We want our choice of fruit and vegetables, year round. We want our choice of seafoods that we've long since depleted our own stocks of. So a lot of the food we do export is done to cover the imports of anything offseason.
We have everything we need to be truly food independent. Except the actual will to be independent. And I'm not talking about on a governmental level - This stuff is straight down to the consumer. Most people want to consume extremely inefficient meat and dairy. Most people want to consume off-season fruits and vegetables. And most people want to consume products that, in many cases, we don't actually produce ourselves.
As much as the average American consumer might claim to want cheap food, their purchase habits show otherwise.