Because the Cubans that fled were the capitalists and landowners whose land Castro appropriated and nationalized. They didn't like that the Batista gravy-train was coming to an end, and their way of life would no longer be acceptable in Cuba, so they fled "oppression."

So when the GOP misuses "socialist" and "communist" to scare people, it really works on those people because they think the government is literally going to take their property away.

Many Cubans in Florida either fled Cuba following the Cuban revolution or are the children/grandchildren of those who did. Those that fled obviously disagreed with the Castro regime so vehemently they left their homelands, friends, and family behind. Very often they were the middle, upper-middle, or upper class of Cuba, so when the socialist revolution nationalized private property, disrupted private businesses, and seized private financial assets, the Cubans that fled were the ones that lost the most. Others fled due to political persecution and imprisonment, censorship, etc. Cuba, like anywhere else, wasn't and isn't idyllic.

The people who left Cuba after the revolution hated Castro and the Communists. Many volunteered for the failed Bay of Pigs invasion. They indoctrinated their children.

https://en.wikipedia.org/wiki/Bay_of_Pigs_Invasion