I think it's a practicality thing, less to manage. Hair can get in the way. Back in high school when I had a ponytail, I used to lift weights on my dad's equipment. He was doing squats one day, and one of my long hairs was on the bar and got caught in his throat when he inhaled. He had to put the weights back on the stand while avoiding the urge to cough. I nearly killed the guy!