Where one sees spurts showing great potential others see inconsistent play.
Williams is at a point where he should be establishing his style of play, and he hasn't done that on a consistent basis. Its not hard to occasionally put up big numbers on lottery teams (Willie Burton dropped 50 for the Sixers before), many nights you don't get the other team's best effort.
Consistency is the key, and Thompson has been reliable and steadily getting better.
Its ironic that messageboard hacks can see that Williams is a great 4 but the Wolves and all the guys who are paid to study the game don't act on it. If he was a great 4, he would have made a spot for himself and they'd find a way for him to play more 4. Teams don't sleep on assets, and the Wolves would love to trade another black asset for a white guy.