I think Snyder's selfishness stems from him getting so few minutes that when he does play, he has to make an impact of can expect even fewer minutes. He's shown promise when he gets decent minutes. As far as making bad plays, if we went off that, nearly the whole squad would sit the bench.
If he's as bad as everyone is saying, why did the Rockets even go after him? Seems like another poor decision by the front office and waste of a roster spot. Why didn't they keep Kelenna Azubuike instead?
I'm not a big fan of Snyder's... BUT, you have to consider some of the facts pointed out by the OP that do make you question why he doesn't get more PT. He's a horrible shooter, but as has been pointed, so is everyone else. He doesn't drive enough, but neither does anyone else. He's not the best ballhandler, but aside from Tracy and Rafer, neither is anyone else. And he does seem to give some good energetic bursts. Luther is still the one that confuses me the most. I think he is playing way to hesitantly, primarily because Rick hasn't helped him enough. Luther seems to be able to drive occasionally (off Yao entry pass, or taking his defender), should be able to hit his 3s if he's more comfortable, etc. But he seems to be confused as to whether he should shoot, or drive, and thus is stuck doing neither, then passing the ball (occasionally poorly) to the next guy, and he'll never get past his deficiencies (he's NOT a PG and can't play defense on SG's).
I don't think anybody knows what type of player he is. Every now then he'll throw down a big dunk or shoot a three, but never consistently shows his game. We know he's quite athletic, but that's it.