Why are trucks going to Mexico? To be refitted as weapons?
Primarily to be used.
They steal a lot of reefer trailers too. I've heard of them backed up to houses and used as air conditioners.
If it's not nailed down, someone down there will steal it. I've picked up trailers from bonded yards that have had all the lights and glad hand grommets swiped. I've had new tires stolen from trailers and replaced with uninspectable garbage.
That's just from bonded yards in Laredo.