When the US imposes economic sanctions on another nation, Uncle Sam is trying to starve the foreign government without starving the the civilian population. To this end there are certain loop holes built in to the sanctions for things like food and medical necessities. Think of it as siege light.
While I haven’t done a lot of heavy research into it, I have never thought our sanctions were all that effective. If they were, then I’d think after half a century Cuba wouldn’t still be communist. But if the theory is that these sanctions are effective, then why would we give our corporations the ability to work around them?
I see the answer to that question being either we realize that sanctions are just a token gesture, about as effective as a strongly worded letter, or our representatives care more about lining their pockets with corporate contributions than actually stopping totalitarian regimes.