Junk food economy

Why is junk food cheaper than natural food? Why is junk food more widely available than food that is good for us? One of the Hostess Twinkies, made in bakeries and packed with sugar, salt, and cholesterol, costs 25 cents which is less than an apple growing naturally on a tree. The cost of apples which are grown organically, without chemical fertilizers and pesticides, is even higher. A USPIRG