But it would be very extremely unlikely that BOTH a globally mobile 30 something and 40 something woman did not have one (especially since we know they did have at least a phone to call for help when they were lost).
In addition it is quite implausible that somebody would set off on an 8 hour trip without having either a good understanding of the route, or some means of navigation (map, GPS, Smartphone etc).
I was happy to trust the story the first time around, but now we know that story was falsified, my trust is gone.
A very simple explanation is that they were distracted and stuffed up. Distraction caused by bereavement, or weather or an unfamiliar vehicle or just because they were having a natter instead of paying attention.