It's not a cry you can hear at night, it's not somebody who's seen the light...

Probably, but everyone was headed towards the main doors (which are far larger than a back entry anyway, I'm sure) and panicking that they were closing. If they had actually continued to close, there would have been mass panic, not people calmly thinking about other exits. We had our entire city fall down. People aren't calm and rational, they're panicky and terrified. The people who worked there were herding everyone out because the evacuation alarm sounded. No one needs a panicking crowd! So holding the door open, especially since it shouldn't have closed in that instance, just seemed like a good idea.