Or someone ahead of there spent several seconds pushing bags out of the aisle, and not everyone realized the speed of evacuation was being determined by obstruc

Or someone ahead of there spent several seconds pushing bags out of the aisle, and not everyone realized the speed of evacuation was being determined by obstructions. Or, not every piece of luggage causes the same slowdown, and the first piece of luggage with significant delay caused the choke point for all of those who didn't make it out. Or a dozen other scenarios. We just don't know. 90% of highway traffic jams I drive through end up having no visible cause. That doesn't mean that there was never anything in the road causing a slowdown.