I think the reason for the open transom is that these boats are so 'wet' that they spend a great deal of time with huge amounts of water sloshing into the cockpits, and that's the only way to get rid of the water.
I'm like you...I find crew safety a real concern for boats like this, but then they routinely never go where real sailors dare. These hot rods go race around two markers in light wind. If the wind gets above 15 knots, they start looking for a hole to crawl into.
Would I dream of cruising something with an open transom? Not during this lifetime or this galaxy, thanks.