I think there is an old AC on this... when crossing a RWY you should turn on every available light. You are right that it is not like a crossing guard for train tracks, but it is part of the methodology of safety. When I reach up and turn on the lights it is just another signal to myself that checklists must stop and all eyes are looking outside up/down the runway. After crossing, the lights come off and we can return to unfinished business.