That which you can attribute to stupidity.
People were panicking over stolen dirty bomb material, only to find that the guys seemed to just want the truck. They opened the extremely-packaged material, went "what's this crap" and threw it away, and will most likely die of radiation exposure. The truck and crane are probably valued at around 10k by virtue of Mexico level of maintenance. How much would various terror organizations have paid for such a haul, so near to the US? I'd wager significantly more than the value of the truck, if they had it.
So thanks, stupidity! We, the not-dirty-bombed people of the world appreciate your efforts in this particular instance!