Any answer to this will be an oversimplification, but my short answer is increased poverty makes for more people with unfulfilled needs. With holes to fill as it were. Food fills that hole. Not perfectly, but enough that people use food in place of what actually fulfills. But food is only a substitute, so it doesn’t sate. There are many things people can substitute for what’s actually fulfilling, but sugar is the cheapest “drug” on the market. The same dynamic is a huge part of what underlies the opioid epidemic.