That's because they are only being used for short hauls. Studies have shown that they are no less safe than short haul trucks in any other part of America.
People who argue that companies in Mexico are going to ship their goods long distance in unsafe trucks are as irrational as people who claim that hundreds of millions of slaves were thrown over board and lost because slavers used unseaworhty ships.
Would you ship five million dollars worth of electronics parts in a truck with bad brakes? DUH!
You must know nothing about the trucking industry. I have watched the junk trucks bought at auction in the states and then seen them transported to the border.
If you would stand at the border crossing and look at all the old junk coming from mexico, that are former US companies worn out trucks, then travel to the Ambassador bridge at Detroit and see the difference your would have some comprehension of the subject as it applies to safety alone.
Oh really, Route 1 in Northern Mexico is the only route from interior Mexico to Baja California, that is not a short haul. Go stand beside Route 1 for a couple of hours and see what goes by.