Why was Cuba the only Communist island in that sea?

Dictatorships take many forms. Cuba isn't the only dictatorship in central America.

See the situation in El Salvador. 🤷🏻‍♂️

There has never been such a government as "communism"!

Not even Marx had a formal proposal. Only a vague idea with no details. Basically wishful thinking and much of that based from Hegel.

Engels formalize the dictatorship in communism.

The older I get the more I care about politics; I understand Cuba is generally seen as Communist but it is/was really a dictatorship with a hefty chunk of Socialism thrown in so a Social Dictatorship if you like. Not many countries fall under the traditional definitions of government any more.