I volunteer to teach hunters safety course in NY. The reason I was given by a DEC official who trained the trainers for the safety course was that a barbed head with blades at an angle less than 90 degrees cannot be pulled through the entry as easily as those that are not. They are worried about 2 things, 1 breaking a blade off and the hunter injuring themselves when field dressing, and 2, the arrow won't come out of the animal which can cause multiple things (like death). That is the genesis of the law.

Not that we are trying to do that (cause death)or anything....

But, in any event, that is what I was told and whatto teach.