I'm guessing it's a lot of casuals who never watched any of these players and just looked at basketball-reference. The main, number one, and primary reason you get Stephon Castle is defense, and most of these people don't understand that there are two sides of the court.
Timvp is kinda looking at some of the wrong stuff, too. With Clingan and Castle on the floor together, UConn's defense was incredible. When you dropped Clingan, those possessions moved down to very good. Thing is, when you dropped Castle and only had Clingan, the defensive rating went to about the same very good spot. What does this mean? A dominant defensive center in the NCAA is a massive anchor, but UConn was just as good when it was only Castle out there. Obviously the team defense was seriously good, but those were the two anchors.
And when Castle and Clingan played together, they were stifling.
What everyone misses on Castle is that you're getting a potentially elite defender, possibly a Jrue Holiday type who is actually taller and stronger. What's more, Castle has good handles, good vision, rebounds, knows how to play the game, high character, high work ethic, a winning pedigree already.
Obviously you rate this guy high in this draft. He'd go high last year - where Anthony Black went, one or the other. Anyone who has him past the midpoint of the lottery simply doesn't know what they're doing.