If a person is breathing why would one apply CPR?

Yes, I can see why you find that confusing. The mistake you're making is to infer that not doing mouth-to-mouth must mean they're breathing just fine, but that's not actually the case. read more

If a person is breathing there is no need for CPR. Cardio Pulmonary Resuscitation (CPR) is performed when the patient is not breathing and has no pulse. A patient will loose breathing before loosing a pulse; if not breathing but with a pulse Expired Air Resuscitation (EAR) should be performed. If no breathing and no pulse then CPR is required. read more

Breathing: Breathe for the person. Rescue breathing can be mouth-to-mouth breathing or mouth-to-nose breathing if the mouth is seriously injured or can't be opened. With the airway open (using the head-tilt, chin-lift maneuver), pinch the nostrils shut for mouth-to-mouth breathing and cover the person's mouth with yours, making a seal. read more