I think Randolph just doesn't have the BBIQ, and more importantly the drive to be a quality NBA player.
Flynn should never have been drafted in the lottery, and is just not a quality player. He rode some big tournament games to a high draft pick, despite the fact that he is essentially a less explosive Nate Robinson.
Thompson is Mark Blount with less attitude...and less defense. He basically is what he is. He is too soft, and not skilled enough to be anything better than a rotation player on a bad team IMO.
Turner is another matter. I am a huge Turner fan, and think he is going to be a very good NBA player. He still needs to work on his shot, but once he gets in a better situation (he duplicated Iggy way too much), he will be an All Star caliber player. It will be interesting to see what Philly does with him though. I am sure they know what he can do, but he also is just a bad fit. I think he would take a lot to be traded though.