It's to stop people standing in the elevator and blocking access by everyone else, the same happens with the elevators from the hanger to the concourse. If some players wanted to play annoying crew members they could take an elevator each up to the concourse and then just stand there keeping the elevators on that deck, trapping everyone else in the hanger area, the same with the command deck elevator, someone could leave the command deck and then just stand in the open elevator, so for areas where there could be problems you get booted from the elevator after a few seconds of waiting.