Probably for the same reason that Germans escaping the Worker's Paradise that was the German Democratic Republic (aka East Germany) weren't big fans of the communist dictatorship that tried to murder them for wanting to emigrate and was extremely corrupt, extremely authoritarian and often looked like they missed the point of 1984 and read it as an instruction manual.

The Cuban Americans in Florida are strongly opposed to opening up to Cuba. To get their support Republicans tend to be opposed to these changes.