I think beucause the main idea is to only get them if you absolutely have to have them because they can weaken your wrists and a lot of coaches prefer to have their gymnasts not wear them bc of that reason. Also they are pretty expensive. If you get hurt and injure your wrists then that would be...
I would get tiger paws if I got any wrist supports but my main concern is that they will weaken my wrists so much, skills on beam will be a lot more hard and painful