The times I've seen it happen will suffice
Of course, it should go without saying that nobody should walk away from the pump for much longer than it takes to fill the tank, if only because it's a douchy move to tie up a gas pump for longer than you need it. But if shutoff failures were anywhere near as common as you seem to think, the latches would be prohibited everywhere.
Lung cancer is extremely rare, regardless of your risk factors. Yet people are still told not to smoke because of the risk increase over it.
A temporary oversight, I'm sure.