In a truck you can't just... drive anywhere. There are designated legal routes that you can't deviate from under most circumstances. The vast majority of food you have access to as a trucker is gas station/truck stop food and fast food attached to truck stops. You have limited cooking options in a truck, maybe a small waffle iron, rice cooker, or microwave. Most won't have room or power for something like a refrigerator (some might, it depends) so keeping non-dry food isn't really an option.