The Cuban Baseball Federation isn't some independent, autonomous athletic association. It is nothing more than a bunch of former beisboleros who front for the Castroists.
Under this "deal", the Cuban players are allowed to return to Cuba at their leisure to visit family and friends, providing the Cuban Federation (ahem... Communist government) is paid off. Without a doubt, this payoff comes against their wages. If history has shown us anything, it is that the Cuban government cares only about two things: staying in power and hard currency.
No other country requires such a bribe in order for their players to play in the MLB.
If the Castroists were had a sense of "morality" at all, every dime made by these players would go to the players, and they would be free to come and go to their homeland as they saw fit.
Make no mistake: It is the Cuban government that requires their beisboleros to defect, not the United States. The same thing is going on with their medical missionaries.