Why was Cuba Communist but not other Latin American or Caribbean countries?

What happened in Cuba was a violent reaction to Fulgencio Batista regime (with business interests in drug, gambling and prostitution through American businessmen in Havana) that was brutal. Communist take over under Fidel Castro with an active Che Guevera, was inevitable.

Well, just to add, other Latin american countries had Marxist / communist /socialist leaders as well. Sometimes these governments did not last because of corruption. Other times they were subverted by other countries. The USA originally agreed to acknowledge Castro as the leader of Cuba and the recognize the communist government. They later retracted their recognition because they felt that giving legitimacy to the communist government could cause the socialist mentality to spread to the rest of Latin America.

Fundamentally, Castro has managed to remain in power in Cuba because he has popular support and he has international allies. Some of you might find this to be a controversial statement, but it is the truth. Recent history has shown that any leader who is too heavy handed will ultimately be overthrown by the population. This never happened in Cuba because Castro is a relatively kind leader and is honest in his intentions to help Cuba succeed. Furthermore, corruption is pretty low in Cuba and Castro does not abuse his power or recklessly spend the country's money.

An 'accident of history': the Cubans who were Marxist succeeded in taking control of the country and remaking the country according to their system. The Marxists in other countries just did not succeed in creating anything that threw down the various governments that were in existence there. Those governments went on in control of the power in the country. Various reasons for that, all depending on the country (and the people at the top of the power-pyramid at the time) that you're taking about in the Americas....

Castro had approached the U.S. following the end of Batista's fall, but was ignored. Castro turned to the USSR and found it a country willing to buy Cuba's sugar production. No other Latin American country developed a Marxist government willing or able to connect with the USSR.

Cuba is an island that fell easily to a communist take over. The Americans allowed it to happen.