My theory on why Marleau gets playing time is because he's seen as an inert, nothing will necessarily go wrong while he's on the ice kind of player. Kind of up and down on his own wing, shuffles the puck along, adequate engagement along the boards, chips it into areas, sometimes gets a shot off.
Not that bad when you're nursing a lead and rolling lines but completely counter productive when you're chasing.
No speed, no explosiveness, no vision, nothing with the puck, muffin shot, no touch in close. Disengaged.