Why didnt cavs draft derrick williams?

they should have got williams for his immediate scoring in the post and three point ability, then they could have grabbed brandon night or kemba walker with the fourth pick both who have proven they could play more then kyrie irving who played in only 11 games , you cant judge a player off 11 games and think he deserves to be the number one pick, and derrick williams was the only player that is even has a shot as being half as good as lebron james so why not pick him