It's a reflection of the idea that if civilisation collapses to the point you can't obtain food except by pulling it out of your emergency store a year later, you're probably going to have died of disease, injury, thirst, violence or a number of more pressing concerns.
Seriously, if the ability to get food to people has been down for a full year, you won't have medicine. You almost certainly won't have fuel, electricity, public order, sanitation, or clean water.
One thing that I think is frequently overlooked is that a person with a year's worth of food stored up also has enough to feed the whole neighborhood for a week if necessary, which might make a really big difference for a lot of people. Having the goods gives you a lot of flexibility and might take some of the pressure off of emergency relief services. I try to keep far more of the basic things on hand (first aid, food, and water purification stuff) than I think I'll need just because I know most people don't, and I live in a place with a moderate risk of catastrophic earthquakes and tornadoes.
Seriously, if the ability to get food to people has been down for a full year, you won't have medicine. You almost certainly won't have fuel, electricity, public order, sanitation, or clean water.