Doesn't defend well. Doesn't rebound well. No good highlight reels. What's going on
Big men take a lot longer to develop in the NBA then other positions. Unless you are a guy with talent like KAT, AD etc it's going to take time. Look at Timelord. He's developing but he still needs another full year to really be a guy who can give you 25MPG.
And Robert came into the league a year older than Bamba did, having stayed for a second season at Texas A&M.
These sort of kids are young, skinny and used to succeeding all through high school and much of college based purely on being way taller and more athletic than everyone else. Suddenly, they have to learn how to compete against grown men who are just as athletic, way more skilled than any competition they'd faced before and far more physically developed.
Not every kid is going to be able to make the jump, to be able to develop into an NBA player. But you do need to give them a little bit of time to see if that will or won't happen.