I believe it is also because when they have concerts there they hang all the speakers and lights from the ceiling (referred to as "flying"). So there are cranks and lifts or supports for cranks and lifts in the ceiling to accommodate those events. They do this with the video board for basketball games.
All the flying is done from the beams and girders in the attic, between the ceiling and the roof. Nothing is attached to the ceiling itself. All there is in the ceiling itself are cut-outs for the cables to pass through. The mercury vapor light units sit in cut-outs in the ceiling, but are also attached to support beams.