It's interesting, the mind set of humans (and some animals I suppose), there seems to be a slight reluctance on the part of the early exiters at the front right side slide, to get going, but once they have, then people seem to be streaming down. Maybe if we have any psychiatrists (I'm sure we have many of the amateur variety) they might be able to explain this.
I'm sure my old horse would have stayed in her box in a fire - even if the door was open - animals ( including us ) have great trouble resolving dilema.
I dealt with office design in a previous life and took part in some interesting research concerning evac from buildings. In experiment, unknowing members of the public were invited to an office very clearly marked with fire exit signs, while they were filling out forms an alarm sounded, the resulting videos were also quite alarming as the volume had to be increased to the level where no one could ignore it and even then folk only slowly reacted while others continued to complete their forms before attempting to leave - then very few left by following the fire exists - they mostly went out the way they came in.
Just how this would apply to fire in an aircraft I'll leave for others but it would seem that many people have difficulty in leaving their seats even when it's pretty obvious that anywhere else would be better.