Probably because of less preservatives? Maybe they shouldn't have such a long shelf life.
I cook for my dog. He eats what I eat. I figure there was no canned or dry pet food 100 years ago and pets survived. Nothing wrong with feeding them "people" food. Of course foodstuff which are dangerous for pets are not allowed in my house...except for chocolate.
I do have dry food available for my dog but she mostly eats what we eat.