Except that the main ingredients of dog food, the dry variety, are bones, heads, feet, skin and organs that humans generally don't consume in large quantities like lungs and intestines. The only time you are going to find things like liver, heart and tongue are the surplus can't be sold for human consumption because there isn't enough demand. Plus the 4F stuff that the processors aren't supposed to be selling for human consumption anyway.
Save a life. Adopt a greyhound.