I think teams in general would not want to sling it down the line on first phase, as all that does is allow the defense to drift and steal the ball of a (by then) isolated winger, and forces your pack to run sideways all over the pitch all day long.
Thus, the defense has to think you are going to try to break through well before it gets to the winger, whilst at the same time they have to leave someone covering the winger.
So, for teams that can't hang on to the ball (read Wasps) who often get no further than first phase, it will always appear that the centres do not pass. Just saying.