It is not accurate to blame the problem on campers and RV'ers. Sure that is part of the problem, but industry stands to bear the brunt of the blame in my opinion.
Pallets and dunnage is normally built and supplied by mom and pop mills,and built out of whatever local trash wood is available.
There are a lot of Amish and Mennonite pallet shops that make Apple and grape pallets. And I would guess at least around here they mostly use black Walnut as that is our dominate species.
There is a Mennonite guy, makes grain augers, subscribes to Henry Fords business model. Keeps all he can in house. His dunnage is milled from his own wood lot in his own mill by his employees. None of this wood is dried ands much of it is green.