NBA question - why doesn't Marcus Banks stick?

Marcus Banks is an NBA player who puzzles me. He's supposed to be a great defender; in one game when he was with my Phoenix Suns, the Warriors' Baron Davis torched them in the first half, but in the second half, Banks went in and pretty much shut him down. I simply blame Mike D'Antoni (a horrible coach) and... show more Marcus Banks is an NBA player who puzzles me. He's supposed to be a great defender; in one game when he was with my Phoenix Suns, the Warriors' Baron Davis torched them in the first half, but in the second half, Banks went in and pretty much shut him down. I simply blame Mike D'Antoni (a horrible coach) and his snubbing of the bench for Banks's irrelevance in Phoenix; but to my surprise, he can't break through in Miami either.
Why doesn't a player like that have more success, if only as a role player? Does he have bad luck, or a bad attitude?
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