[dedward]

Because they have no shortage of cash to crank out new subs, and no shortage of very poor people willing to risk the journey on the chance of success. It's the simpler solution.

Plus, subs are inefficient - the regular drug busts around here (central america) , when they find them, are regularly into several metric tons, usually on boats that are inspected while refuelling. That's just what gets caught... which has to be a very small fraction of what passes.