Probably because the battle is not over yet. I'm sure there'll probably be another boss battle with Madara later on in the game. Assuming they get that far at least.Wooooow that was cool of tsunade but still i dont get why she just released a part of her yin seal and dont use her complet byakugou
Anyways:
Tsunade went H.A.M. Many tears were shed, when she used that Creation Rebirth + Heavenly Kick of Pain combo on Madara. Awesome