That got me thinking - when I used to work on the rivers (G2/3 white water in canoes), we tended to run with helmets all the time on even the flat sections. What that meant was that you weren't tempted to just run a rapid without your helmet on because "She'll be right, I've done it already this week, and twice last week... and the week before... and the month before" - and I suspect that the "out the vehicle = hard hat" on is an extension of that. One of the other things is just avoiding forgetting things - even now, I have habits from that that have carried over - helmet on ready to go on the motorbike? It's strapped up... not just sitting there, as soon as it goes on it gets strapped up, as it's too easy to forget.
Just remember half the population are less than average intelligence... we see it here in Australia, especially at tourist traps that have got a reputation for photo opportunities - people climb over fences etc, stand in the way of the waves or blow holes...