People move to areas with better material conditions. Assuming that is the fault of Socialism and not of countries being in different stages of development is immaterial and ignores the trajectory of nations, as well as the geopolitical landscape.

For example, in the GDR, education was high quality and free, but wages were lower than in West Germany. Many highly educated people in GDR attempted to leverage their free education for higher wages in the West.

As for Cuba, people fleeing are typically the people prosecuted during the revolution, ie plantation owners. People still flee from less developed to more developed countries, which is why people flee from Capitalist states to other Capitalist states.