Because someone has to know how to grow the potato or raise the cow or plant the corn. Right now we (modern first world countries) export that to fragile processes far away. Generally at great cost, environmentally and to the people/countries we export form. See the Amazon rainforest, slave labor in China or Africa, or un-controlled overfishing.
You sure? I'm in the Midwest and absolutely surrounded by farms. Do you really think your beef, grains, and potatos don't come from the heartland? How in the world would that make sense?
Yes the US supplies the majority of it's food. I was talking about the first world countries in general. Second the monoculture farming system the US is using creates HUGE environmental costs, it's not just about import/export. Beef feed lots with thousands of cattle packed together, chicken and pork farm pollution, monoculture (corn and soy beans) destroying soil, pesticides polluting and killing river ecosystems, and up to 40% food waste. All products of the JIT food systems. The rest of the western countries (except Canada which is similar to the US) are mostly food importers generally from the Global south (with Russia and the Ukraine also supplying quite a lot). I grew up in the midwest in a family of farmers and my wife grew up on a working small cattle farm. There are MAJOR issues with the US system, generally it's not the import/export part though. That's more of an issue in European countries (the Netherlands seems to be the major exception here). Palm oil is also a major factor in rain forest de-forestation, which is a major import in many countries:
