Okay, HARDLY anyone comes back from there, even though there are some very good players there. For Bradley, all rookies need minutes in the game to develop an NBA game.
Some notables:
Rafer Alston, Louis Amundson, Chris Andersen, Kelenna Azubuike, Matt Barnes, Devin Brown, Will Bynum, Matt Carroll, Eddie Gill, Stephen Graham, Jason Hart, Chuck Hayes, Anthony Johnson, Dahntay Jones, Jamario Moon, Mikki Moore, Smush Parker, Bobby Simmons, Ime Udoka, Von Wafer, C. J. Watson, and Mike Wilks.José Juan Barea, Brandon Bass, Andray Blatche, Aaron Brooks, Jordan Farmar, Marcin Gortat, Ramon Sessions and Martell Webster.
All played in the NBDL, and have had a successful NBA career.
And you are right, guys need to play to develop. But playing them in the NBA before they are ready can do more damage than good. That is why the NBDL is there.