Why do foods like dry soup mixes remain un spoilt for many days?

Spoilage in foods is due to fungus or bacterial growth. Dried soups lack water and so form a hostile environment to those organisms. Other methods of preserving food from spoilage include adding salt, adding sugar, adding vinegar canning, or irradiating the food. These last two kill any spoiling organisms inside the food, so until the food is removed from it's sealed package it doesn't spoil.