Because he's thin?
I heard about some guy who played for the Pacers a few times, rail thin is how they described him coming out of college, too. Never got bigger. Maybe my memory is cloudy but I think he had a pretty OK career.
Everybody isn't going to be a starter from this draft. Some guys will have injury issues, some guys will struggle on defense, some are just overrated (Noah, for example).
But it's still by far the best group of players in the draft in a long, long time.