Cuba is still a communist country. It's not socialist, as socialists embrace democracy. The same regime that tried to get nukes is still in dictatorial control of the island. Apparently, we cannot invade and nation build for a variety of reasons perhaps including deals involving the Crisis. If the Cuban people (meaning, those living in Cuba) want Americans to visit and buy their stuff, then they can become a democracy. We exercise serious economic warfare against Castro's totalitarian regime, and we should. Perhaps someday, the regime will be weak enough for the people to rise again.
1. Western democracy, especially outside the US and Europe, is a very new thing in history. We were among the first and many countries are only having democratic revolutions today. Many have not had such a revolution, and they continue to live in political darkness.
2. We cannot invade and nation build every country at the same time. There must be priorities and nations with the resource and infrastructural capacity to nation build themselves to a considerable extent will be at the front of the line.
3. We can invade tyranical countries by engaging them in diplomatic and economic spheres. In this way, a crack is opened for our influence even if there is not immediate and dramatic change. It's a slow method, one which I personally do not prefer, but it is a means.
For the above three reasons, and others not mentioned, many (most if not for Europe) US "allies" were undemocratic regimes. Now, counting them today I figure the vast majority of our allies would be democratic.
I reject that reasoning. People very rarely, if ever, give up their freedom and vote in a tyrant knowingly. People want to have a voice in their authority - everyone does. It's animal and human nature to desire control over one's resources and decisions. Claiming that some people like being slaves and want to remain so (or that they don't know better thus they are happy) is not something for me.