Why are pivot punches illegal?

Its a foul outlined in the rules of boxing, why is it illegal? Mayweather used that against Hatton and didn't get DQ'd. But why is it illegal? A foul is an action by a boxer, identified by the referee, that does not meet the standard of a fair blow or the conduct of a responsible professional fighter. Fouls may include, but are not limited to, the following types of contact or acts: 1. Hitting an opponent below the navel or behind the ear; 2. Hitting an opponent who is knocked down; 3. Holding an opponent with one hand and hitting with the other; 4. Holding or deliberately maintaining a clinch; 5. Wrestling, kicking or roughing; 6. Pushing an opponent about the ring or into the ropes; :lol1: 7. Butting with the head, shoulder, knee, elbow; 8. Hitting with the open glove, the butt or inside of the hand, or back of the hand, the elbow or the wrist; 9. Purposely falling down onto the canvas of the ring without being hit or for the purpose of avoiding a blow; 10. Striking deliberately at that part of the body over the kidneys; 11. Using the pivot blow (pivoting while throwing a punch) or the rabbit punch (punches thrown to the back of the head and neck areas); 12. Jabbing the eyes with the thumb of the glove; 13. Use of abusive language; 14. Unsportsmanlike conduct causing injury to an opponent that does not meet the standard of a fair blow; 15. Hitting on the break; 16. Intentionally spitting out the mouthpiece; 17. Hitting on or out of the ropes; 18. Holding rope and hitting; 19. Biting/spitting; 20. Not following referee's instructions; 21. Stepping on opponent; 22. Crouching below opponent's belt; 23. Leaving neutral corner; and 24. Corner second shouting http://www.abcboxing.com/documents/abcboxing_regulatory_guidelines.htm