The thing to remember is how the US enforces the embargo. Any ship that docks with a Cuban port is blacklisted from docking at US ports, and the waters around Cuba are coincidentally heavily patrolled by the Coast Guard in the name of "drug enforcement", and of course Cuban money is heavily restricted in international banking.

So, while the US has technically left the door open for food and medicine to go to Cuba, like so many other things the real oppression is not the letter of the law but the free hand of the market. Docking at Cuba just doesn't make economic sense unless you're ship is being paid by a government (ie when China sent a bunch of trains to the island) enough to offset the opportunity costs of going elsewhere.