The thing that makes these bags different from other food storage bags is that they are a powerful barrier to oxygen, light, and moisture. It blocks all these from reaching the food and thus prevents it from spoiling.
An oxygen-rich environment destroys the food via oxidation, facilitating the growth of mold and aerobic bacteria. This changes the color, smell, texture, and flavor of the food, thus leaving the food not to be used ever in the future.
Moisture and light also kill the food by allowing the aerobic, anaerobic bacteria, and molds to grow.