Dogs recognize food as a reward. We don't have to tell them that food is a reward, because it's in their instincts. Because of this fact, they seek to work in order to earn their food, so when they don't have to work in order to receive it, they become confused and complacent. Just as people appreciate what they earn, so do dogs. 

If you set a kitchen boundary for your dog and don't allow them to cross that line, you're letting them know that you're in control of the space and that you set the rules. While setting household boundaries in any room is a good idea, as it specifically relates to not allowing your dog in the kitchen, I simply can't argue with the results. I've seen dog owner after dog owner have a drastic improvement in their relationship with their dog due to setting this boundary. 

Dogs who respect boundaries set by their owners are far more likely to respect boundaries reinforced by acquaintances and friends. Another reason why allowing your dog to hover the kitchen space does not help their overall health is that they can easily and many times unintentionally get in your way. You may be unconsciously catering to their boundaries that you don't even know they've set by moving around or tripping over them when you're in your kitchen.

The main idea I'm communicating here is this: your dog wants clear boundaries to follow, and they're looking to you to provide them. The only thing that's lacking in your dogs understanding of your boundaries is clarity. When you are clear with the boundaries and consistent in reinforcing them, your dog is set at ease because they don't have to be responsible to be the pack leader. 

So, why is the kitchen a better fit for people and food than it is for dogs? Because your dog respects the fact that you have exclusive rights to specific areas in the house, and they see you as the leader when you set and reinforce those boundaries.