In the world of hand to hand combat, styles can differ, and perhaps the style with the least variety is boxing. While individual styling can differ greatly in boxing, the technique remain the same as it is considered a single art. In comparison, mixed martial arts is a blend of any martial arts with no hold on strikes (other than dirty techniques).
Due to this blend, you are more likely to see crazy moves such as ridiculous kicks or superman punches. These strikes are rarely thrown, and for good reason. Strikes such as these can make a person highly vulnerable, and all it takes is one well placed strike to do some serious damage. Regardless, sometimes these moves do work because they are so unexpected.