I'm curious how UUV (unmanned/autonomous underwater vehicle) tech might change the economics of that; certainly you could improve on the eggs/basket metric if you could bring the cost/size/detectability down.
For your cruising theory; I wonder just how hard it would be to build a magnetic/quickset-epoxy limpet-mine type construction that can hold a few 10's of Kg of payload. Bonus points for ruggedised GPS+satphone so you can track it, and perhaps even instruct it to detach and inflate buoyancy compensator 10-20m underwater til you come collect.
I'm guessing you could more easily target cargo ships since you know (or can find out where they're headed) and you also know they'll use marked channels. There's no reason the buoyancy compensator couldn't be used to park the shipment until a ship headed the right direction passed over it.
I listened to a talk from the former head of a customs agency who admitted that search alone is useless in stopping the flow of contraband. He described it as searching for a needle in a haystack in a haystack.
The intelligence turns out to be a good method. It is difficult to import multiple kilograms of a drug into a major city and not make noise about it. First you have the concern of anybody in the lower end of the pyramid being caught, and second there is the competition who are usually more than happy to rat you out to get rid of you.
I'm willing to bet that even the case of the professor in OP was a result of intelligence. There are two common ways couriers are caught in South America:
* the first is that they are turned in by the organization that has sent them. As part of police corruption and keeping locals out of prisons they setup foreigners.
* the second is signature detection. It turns out that a lot of organizations use the same types of suitcases. I bet it was the type of suitcase he was carrying that prompted them to search.
1- The 'drug mine' is wildly successful and has not been caught by the authorities yet
or
2- People intelligent enough to be building such devices found less risky and more profitable avenues for their skills. i.e.: criminals are not smart and that's why they are criminals.
I mean, drugs are clearly getting into the US, and proper organizational structure in your criminal enterprise means that mules and runners getting pinched every once in a while is just a cost of doing business.