This is false - if people have the option, they prefer the locally grown, locally owned and operated smaller stores that might cost more, or farmer's markets, or ethically sourced food. If a consumer has low income, or is in a food desert, they don't have the option, and the economics of Walmart mean that there's no way for such a small business to compete unless you're basically running it as a charity, or you're doing something (possibly) on shaky ethical grounds to make up the difference.
We could fix these things by legislating big box stores, preventing effective collusion and hostile pricing, protecting smaller businesses with tax breaks, higher taxes on megacorps, and so forth. It is, in fact, possible, for megacorps to coexist with successful small businesses and this hostile and rank antagonism from big companies doesn't have to happen. They just lose out on .005% potential profit, so it's better to lobby for (and obtain) unchecked influence and dominion over American markets.
Community management and regulation plays a part, but food deserts represent a captured audience or market, so the primary goal is to shut down any possible "competition" no matter how little they actually impinge on profit, effectively disallowing competition. Throw in Amazon's racket, and the whole idea of an American "free marketplace" is more of a sick joke than any sort of principled reality.
You will buy your mass produced stuff from China and Nestle and Coke and Walmart, and you will like it. If you don't like it, good luck, because you've been priced out of leaving unless you're willing to be broke.