Don’t worry. Some is local-brand or store-brand instead of name-brand stuff, some comes from bankruptcies or store closings of other chains, some comes from trial runs of new flavors or new sizes, some comes because it is indeed getting close to the expiration date. But even with that last one, note that the FDA does not have a hand in those dates — it’s up to the manufacturer.
Big Lots sometimes has good deals on groceries. They’ve even brought in their own line of generic foods, with canned tomato sauce and canned veggies due to demand.