Us older folks might remember and think about it this way, what did dogs eat before dogfood became the way to feed? Scraps and leftovers of the family meal. Think about years ago and the life span of dogs. Dogs lived longer. I remember dogs living to 18-20+. Now, you hear about so much cancer, liver, kidney and digestive issues that we never heard about years ago mainly because the commercial dog food companies began to put profit over quality and safety.
The first dog food was canned horse meat, but over time and only within the last 40 years or so, became the dry, extruded, rendered, corn filled, crap that it is now. Read the ingredients on a bag of dog food, what are some of those things? Meat Meal? What meat? Beet Pulp? Look at this list of ingredients to avoid: http://www.dogfoodproject.com/index.php?page=badingredients. Who is going to remember all this when at the grocery store? Yet all this crap is in many of the top grocery brands and even in those foods often thought about as premium.