You guys arent the ones fighting in that cage, so it doesnt make sense why you should tell what is more effective to them.
Kneeing the body, or striking the head? The goal is to end hte fight quickly. Head strikes usually do that, as opposed to a body shot. Again, this has nothing to do with the UFC blah blah blah. The fighters chose not to utalize it. So be it. At least the UFC allows elbow strikes...