A Night at the Movies

I was standing in the longest line there ever was waiting for popcorn and I looked over and noticed a woman. She was at the counter ordering and she had a tray to put her food on, she noticed some stray popcorn kernels left over from the last person so she tipped the tray and spilled the old popcorn onto the floor. Why is it that this sort of thing is acceptable at a theatre? If she were at home or even a restaurant she wouldn't dump the food she doesn't want on the floor.

Example number two - look around a theatre after everyone has left, food containers everywhere! Why is this a place where no one feels like they need to clean up after themselves?
I don't understand how people's behaviours change so much once they enter the movie theatre.
L