He runs himself into traffic way too often. Watch Eriksen; similar build and style; opens up space, plays the pass early and doesn't dribble for dribbling's sake. Gets all the benefit out of the dribble in the opening few strides, whereas Januzaj wants to keep going or hasn't fully beaten his man at first.
Essentially Januzaj cuts off his angles and options while dribbling, so despite his passing being great for his age, he's working at a severe disadvantage compared to players like Silva, Hazard, Eriksen and Di Maria, who open the pitch up and created channels for the players around to run into.
This is the reason I'm not sure about Januzaj through the centre yet (even if Rooney, Mata and Di Maria weren't there), though he's more suited to it than the wing. He runs to one side or the other, like a swimmer who can't stay in lane. So even centrally he will box himself and hand advantage to the defensive midfield.