Why do chocolate flavors have less protein than vanilla?

To achieve a rich chocolate taste, cocoa must be added along with a chocolate flavor. Vanilla only requires flavor for a good taste. The added cocoa, about 1 gram per serving, displaces some of the protein in a formula. Various brands deal with this lower protein situation in one of two ways. Either their chocolate product will have slightly less protein and slightly more carbs, or the serving size is increased to make the protein level constant between flavors, but there will be fewer servings.