I'm not excusing passengers getting off the plane with their belongings, but it's also not surprising when there are first person stories of $3000 laptops going missing after the Southwest accident in New York.
If the plane isn't on fire or in multiple pieces, it's not hard to see how people would grab their stuff. Yes, it was an emergency, but if it weren't a frantic "get out in 30 seconds" environment, they probably deplaned relatively calmly and slowly.