there has been lots of previous discussion here on this. It should be easy to set up a simulation: (i) evac a plane with everyone leaving carry-on behind vs (ii) everyone grabbing it; and comparing the time. I've said before that an educational video could be made, showing a burning plane and the above two scenarios. Just a cartoon. In scenario two half the pax get fried, in #1 they all get out OK. If this was shown on every flight, then the mob would WANT to leave their bags behind, and would WANT everyone else to leave their bags behind. But obviously airline bean counters don't want movies showing crashes, bad for business.