The temperature of the air is low enough to dry the food, not cook it. It is as simple as that. Keep in mind that food drying is a one-time cost. Canned foods, once opened, must be used promptly, but containers of dried foods can be repeatedly opened, ingredients removed or added, and closed again with no deleterious effects on the contents. There is a movement now away from the importation of foodstuffs, not so much because of safety considerations but because of an increasing awareness of the importance of self-sufficiency when it comes to one's own food supply.
Food drying is a form of creative recycling.
What I like best about incorporating dried foods into my diet is that it allows me to control the quality of the food I eat whether I am at home or backpacking in the wilderness. Dried foods are tasty, nutritious, lightweight, easy to prepare, easy to carry, and easy to use. Many foods are a little darker in color, more fragrant, and sweeter in taste. Do not expect food dried at home to look or taste like commercially dried food. In my opinion, home-dried is much better.