He is 5'9" and 180, that's why.
His talent is undeniable, and he might be able to transition that talent to the NHL. Not surprising his chances of doing so we're limited in Boston.
So what he's small! If Tyler Johnson and Martin St. Louis could make it why not him? Both 5'8" and the same weight as him. Bruins messed up not giving him real top 6 minutes. Really hope he comes back to haunt them!