I think it has more to do with the nature of running in football. I see a few ball players whoi get positive hip elevation after accel phase. Most have to keep their feet close to the ground and their hips low a great deal of the time. I think it becomes a pattern. It’s like taking a 100m sprinter and putting him on a gridiron. I imagine the guy would get smashed until he learned to lower his C.O.G. Then over time I would think that once pretty running stride would get ugly. Also, as far as DB and WR looking better, I would attribute that to the fact that they rarely have to play low. It is more about what you do most often becoaming your dominant movement pattern.