Only because we're on a good run of form at the moment and I think Ole doesn't want to risk losing the momentum in a confident and succeeding squad. I also think Shaw is seen as a player who benefits from more game time rather than less - Ole has said that there will be different approaches for different players. Shaw is more defensively experienced, and we can't afford to drop points at the moment, so that may figure in Ole's thinking. I doubt if it's a matter of trust though, at one point we were wondering if Shaw would get his place back, such was William's impact.
I think Ole will give him a start when he thinks Shaw needs a rest, and he's featured a lot in non-EPL matches, so maybe we'll see more of him in the EL.