No one really gets it. The blood contains a great deal of bio available oxygen. what we do not have is an independent method of moving cells back and forth. That can only be done through varying the blood pressure and that is wonderfully done with chest compressions. It is not done by blowing air into the mouth.
When a person collapses on the street, it is time to jump into action. Make sure someone is calling 911 as no one is able to last long applying CPR. Then check for a heart beat or a breath. If these are missing, apply chest compressions immediately.
You are saving a life and yes, this is the most important intervention.
I figured this all out ten years ago when my life was so saved. I was alone in understanding why I was alive. Now best practice does drop the need to do mouth to mouth. It only took a decade or so.