Who loads the trailer? Rocks on one side and the marshmallows on the other.
The driver is ultimately responsible for the load, but unfortunately more and more shippers no longer even let drivers on their docks, meaning they don't have a lot of control over what the forklift jockeys (who often have little or no clue about proper loading aside from "put the crap on the trailer") are doing.
Yes, the driver could pull out to the parking lot, see it, and simply back in again and refuse the load, but this opens up all sorts of other cans of worms that some drivers are not willing to be responsible for opening. Myself, I've done it - lots of times.