I've been on clipless since Look got their pedal out to the masses -- 18 years ago. I fall a lot less since leaving cages behind because of the instantaneous release. I wonder if the question as to why is more easily solved by who got the person into riding in the first place. My riding friends who got into biking on their own rode with cages far longer than those who started riding with friends who already used clipless. Also, if you're on a budget and just getting into serious biking, the cost of the pedal and shoe can be really significant -- and many newbies just don't understand the advantages of the system.