In a US style democracy, instead of a party's time being spent on running the country for the people, they are forced to compete with other parties in expensive populist contests. Funds come from lobbies, corporations and other interested investors, hoping to buy influence. Once in power, the winning party returns the favors to its financial backers. It also tries to keep sweet with the privately owned media, which makes sure they are pleasing the owners of the newspapers, etc. Public opinion is manipulated, which can sink the party and is designed to facilitate the media owners' agenda. Democracy is therefore nothing to do with governing on the people's behalf, and is a deception that can never allow any socialism to flourish.
While I'm not a huge fan of Cuba, this is still an interesting article about why the Castro's have resisted for so long and are completely content with any US-imposed embargo: