Having grown up in poor areas, people tend to buy things because those are the things they’re used to buying. They are generally not making rational choices about optimal calories per dollar spent or best nutritional value per hour of labor expended in cooking. My neighbors almost all drank, a large percentage did drugs, they were often quite impulsive about purchases, and few of them planned ahead very effectively. My mother got some neighbor ladies together to do monthly bulk shopping at a nearby big-city farmer’s market, saved us a ton of money, but nobody would have done it if she hadn’t talked them into it.

Real human beings are often not rational utility-maximizers. Explanations that assume that they are, are going to be deficient.