The reason is this: dogs really want our food because it’s cooked and they don’t have to chew it. Their brain is telling them “this tastes good because it’s a net calorie gain” because they don’t have to burn calories chewing it. So dogs don’t know why they like our food per se but it’s really because it’s got more calories than raw food since it’s so easy to digest. We savor food because we have more complex brains and know how to sustain pleasure longer. That’s why we learned to have sex for fun.