I believe handle dragging developed in response to stop the beginner from slicing the ball so much and its very easy for teachers to teach this way and golfers can "feel good" if you nail the shot without regard to any optimization of impact conditions.
Of course, if you don't like the impact conditions generated by machines like Trackman and Flightscope, question the machines and don't put up your own theory of ballflight/impact. That's what almost always happens in history. Somebody says the masses are wrong, a few change, the masses beat their drum louder and attack the methodology and thereafter, the masses finally convert.