That is mainly a density issue. Most people don't like density.
At an ordinary population density, supermarkets are about 2 to 5 miles from each other, which is probably 3 to 7 miles by road.
Large stores require many customers in order to remain in business. If supermarkets are closer, then they lose efficiency. Prices must be higher. Variety drops; you'll get just 2 types of cheese and 1 type of apple if the stores have to be smaller.
Without a car, large shopping trips become impossible. A young healthy adult can carry 1 or 2 shopping bags about 0.7 mile without major difficulty, but that just isn't enough. Stores would have to shrink by a factor of 20 to 100 in order to get them close enough, but the efficiency still plunges. Think of the portion of each sale that must support the manager's salary, or the number of stores at which each delivery truck must stop.
Without a car, frozen food can only be purchased in winter. Hot food, such as the fried chicken my supermarket offers, would never be able to get home in good condition.