If you have a business, you learn the hard way not to keep your pallets outside, and if you do, keep them fenced up.
People will come by during the night or weekend, help themselves to a trailer load of them, and take them right to the local pallet recycler. At a buck or two each, that adds up quick.
Does it? That honestly seems like a waste of time unless you're doing 500+ a "job", and the time/energy needed to steal 500+ pallets seems like a negative return on investment. And who has 500+ pallets sitting around unguarded in one place? Enough to make pallet stealing profitable? I'm unsure.
If recycling a pallet was more in the $10-15 range each, I could maybe see the argument.
It falls into a similar bucket as stealing copper from the wiring of abandoned/in construction buildings
Even the trash pickers that drive around all day picking up scrap and might make $100 if they are lucky