There are things like the difference in the cost of a single, reasonable, serving of chicken. Buying a chicken breast is more expensive in price per pound than the family pack of chicken breasts or an entire chicken. Similar things with carrots (I only need 2 or 3 carrots for the meals I have in mind for the week) but instead have to buy the bag for $1 or $2 and rather than one of them for $0.10.
Next there's the issue with single meal variety. Back when I was living with my family, a meal would consist of several different items - some beans, a meat dish, something else. Cooking alone I can't prepare a wide enough variety for a single meal and hope to eat it all (and have the portions be something that is healthy to eat). If I want mashed potatoes to add some variety, I can't make it in the quantity that brings down the price to that of a potato... and so I'm getting single serving cups of instant mashed potatoes. The five pound bag of potatoes is difficult to eat before things start getting funky and buying potatoes in in the "select and bag" tends to be the organic variety which is much more expensive than that 5 lb bag per unit weight.
When buying meat and produce in units that a single person is going to cook before food waste occurs (and causes the effective price to go up) gets to the point where prepackaged frozen (and even weekly delivery!) meals become competitive on price and start having more of an advantage on individual serving variety.