You are correct west lakes but better to take a mini rucksack than full sized handluggage? It is clear that pax will NOT follow instructions. Every evac that has been documented in social media has shown this.
My guess is that, in evacs in previous decades, many pax took hand cases with them - but there were no photographs to prove it. Further I speculate that the professionals (crew and rescuers) who saw that bags were taken did not speak publicly about this aspect.
There are many examples that, in extremis, people revert to their first learned behaviour. None of us know how we are going to react. I suspect a large part of the explanation will be if the evac is notified some minutes in advance with all instructions repeated loudly when they ARE listening. Or whether it's an unexpected evac with (practically) no warning.