In American Football, can you throw a forward pass? Or in Basketball, can you shoot three point shots? Both were not originally in those respective games, and were added. The rules of all sports are evolving, and will continue to do so.
I'm not aware of any sport that restricts your diet, or the amount of exercise or training you can perform. Yet some chemical substances are arbitrarily banned. It is anti-science!
Can you move while tossing the ball in the air repeatedly (dribbling against the sky)?
No.
Wait why? It's just like dribbling except upside down.
It's just the rule.
It's just the rule, man. The rules are what define the game. Why can't I start the bishop where the queen is? It's just the rule. Why can't I have an under inflated ball? Just the rule. Why can't I use a cricket bat in soccer? Just the rule.