Carry on baggage/ Marketing.
One of The reasons why so much carry on is carried is because, in this hurry up world, the delivery of hold baggage to the reclaim is inordinately long. The carrier I worked for had targets of 1st bag on the belt within 15mins of blocks, last, 40 mins. The target for compliance was 90% and we were close to meeting this most of the time.
Other reasons include mishandled baggage and the fear of your bag not arriving. With the advent of reconciliations systems, the mishandling of point to point baggage is remarkably low - our carrier averaged around 1.5 bags per 1000 pax. BUT...transfer baggage is a different matter - usually becuase, wrongly, many transferring carriers put low priority to these bags since the problem of pax confrontation is at a different airport!
So... With this in mind .... Many carriers encouraged (marketed) the acceptance of carry-on baggage sometimes advertising that their allowance was 2 bags providing you could lift them into the overhead lockers without assistance.
The suggestions of locking overheads would certainly reduce the thoughtless idiot blocking the aisle for other escaping passengers but on a risk/cost analysis would probably reject the upgrade required. I liked the suggestion that those who had carry on with them on the ground after the evacuation should be prosecuted but that would be unlikely to happen which is a shame.
It is never to be forgotten that cabin crew are not just glorified waiters/ waitresses. The actions of these and the cockpit crew appear to have been exemplary