Cognitive psychology studies the higher mental processes of humans. These include memory, perception, intelligence, creativity, language and decision-making. Behaviorism is strictly focused on shaping physical behavior with no attention whatsoever given to the thinking behind the behavior. Behaviorists, by nature, are very concrete thinkers. They couldn't care less about what you're thinking.
Behaviorists have no interest in the intangible and invisible workings of the mind.
They are only interested in performance and what you physically do. Cognitive modification, on the other hand, demands much more attention be paid to the intangibles that make us human. The cognitivists are interested in how you process information, analyze situations and make decisions. Since the decision to eat always precedes the actual eating, the decision-making process is where you must make the changes necessary for success. Behavior modification doesn't take into account the consciousness that manages the behavior.