Also, some cargo just isn't nice to have in your passenger compartment. (Bags of fertilizer or pieces of greasy machinery come to mind.) The Avalanche's bed is covered in a tough plastic lining, easily hosed out or just left harmlessly filthy.
But when they actually had a big mouthful of greasy, crunchy, salty, fried potatoes, the powerful gustatory experience caused all thoughts of chocolate or sardines to evaporate.