You've slightly oversimplified here. The US doesn't just not supply... they threaten to punish others who would like to supply, whether for commercial or altruistic reasons, and actively patrol shipping lanes to ensure that these people are not able to deliver food or medicine.
I'm talking about Iraq in this case.
Actually, Castro didn't pick his friends, the US picked theirs. They just happened to pick the guy (Batista) that was willing to kill people to keep unions out of US owned factories. The problem was that the US decided to be friends with the guy who was so egregiously abusive of his power that they managed to alienate the vast majority of the citizens of Cuba.
Finally, you should really read about the CIA, Nicaragua, and the CIA's involvement in the California cocaine trade to raise money for their covert war in Nicaragua. You'll find that there are congress critters that find the idea of a US gov't agency selling highly addictive drugs to US citizens in order to raise money for people with a stated policy of shelling schools and hospitals somewhat... problematic.