Details about ban on travel to Cuba.
Technically, it's not illegal for US citizens to go to Cuba. They are outside of US jurisdiction, and the US isn't legally at war with Cuba. That's the freedom part. Hooray for us! However, it is illegal to spend money in Cuba. The government claims jurisdiction over commerce. The gotcha, for those of you who are saying, "Well, how can they prove I spent money there?" is that the law is written so that spending time in Cuba is considered proof of having spent money there.
But, the law is on really, really shaky ground. It's not really been tested in court as it's applied to individuals. What will happen, if you get caught and choose to fight it, is the US government will press charges. You get a lawyer. A few years, and major legal fees later, they quietly drop the case or settle with you for a nominal fine. But, you still paid a major fine, just to your lawyers instead of the government. The deterrent effect is still there, 99% of US citizens are still scared to go, the law was not overturned, and the Cuban people are still desperately poor because of their bad, bad government.
Why does the US care about Cuba anymore? Is it because it has an authoritarian government accused of human rights violations? Right. That's why they also make travel illegal to China, Vietnam, Saudi Arabia, etc., etc. The government cares because there are a lot of dispossessed Cubans who live in Florida. It's a very important state in national politics, evenly balanced between parties. Those Cubans seem to think that once Castro's gone, they will be able to move back, get all of their property back, and start ruling the country again. They will vote against anyone who even tries to suggest that the days of Batista won't return and we should make peace with the current government.
So, the US will patiently wait until Castro dies, then try to quietly overthrow the communist government. The Cubans in Florida are happy. Whoever gets elected "Leader of the Free World" because he won Florida is happy. The rest of the people in the US really couldn't care one way or the other. The people in Cuba are miserable, but that must be their fault for having a bad, bad government. The world keeps turning.