huju: Sanctions are imposed by politicians, not by diplomats, high-ranking armed forces personnel, or even by foreign policy experts. Politicians on both sides of the aisle crave for the Cuban-American vote (to take one example.) The Cuban-American man on the street demands sanctions. He is no foreign policy experts and neither are the vast majority of the 535 Congressmen and Senators who coded the Cuban sanctions into US law.
Politics wins over the best foreign policy any day of the year.