Transporting a truck of legal goods across a whole continent and multiple countries is much cheaper and easier than a briefcase of illegal drugs.

The total cost of risk-free (i.e. fully insured) delivery of a truckful of goods is trivial compared to even quite cheap products; while that briefcase would pretty much have to double in value after that long trip to make the transport profitable.

That briefcase will increase in value ten fold over the journey. So my point stands, easier to transport the briefcase and the returns are better. The risk is higher but that is why the returns are higher.