He falls down so much because of the way he skates. Bulking up isn't going to make him stop falling down.Does any player in the league fall down as much as Jack? He is one of the best skaters in the league but yet falls down probably more than anyone else - because he is weak.
Doesn't mean he would avoid all injury risk, but getting stronger would make a clear difference. He has yet to make meaningful strides here in the last couple of seasons.