The empire is too greedy for even short-term profit, why make someone a martyr when you can martyr and occupy entire country to exploit forever? It was actually one of the reasons Cuba moved on to imprisonment post-revolution, because making your class enemies martyr unite them. Cuban revolutionaries used to just line class enemies against the wall. It was a little disagreement between Fidel and Che on execution because Fidel wanted to spare noncombatant enemies but Che said line them up.