I think with chains mounted on the trailer tongue at a single point, it doesn't make any sense to cross them. If the event of a hitch failure, the trailer tongue will still drag the ground. Crossing only REALLY works when the chains are connected at the trailer at 2 different points. So, I think that's why some people don't bother with it.
I do cross my chains (single point of contact on the camper). There is a right and left side, with the chains mounted side by side in the same U. But I do that to shorten the chains a little. In the event of separation, the crossing would not help a bit.
Another thing, maybe some people just don't know is safer to cross them? But like so many think, "It will never happen to me... I'm the exception!"