Castro was pragmatic. He realized that any substantial Cuban intervention in the Americas would inevitably invite an enormous and potentially overwhelming response from the United States. As a Latin American head of state, even having a few communists in your cabinet could raise the ire (and all that came with it) of the CIA. Could you imagine the response if Cuba, like they had done in Angola, sent tens of thousands of troops to aid the Sandinistas in Nicaragua? Cuban "meddling" was used by the United States as pretext for its nearly decade-long campaign to reverse the Sandinista revolution anyways. Had the Cubans actually been on the ground in Nicaragua (in any significant capacity) it wouldn't be unthinkable to expect an even more substantial American response, to say nothing of possible direct action against Cuba. I realize this is all quite hypothetical, but not unreasonable considering certain American administrations' interventionist tendencies in the region. See William Leogrande's Our Own Backyard or anything from the Lefeber camp.

Africa was a different matter. It was further away, not considered to be America's backyard. While it was certainly considered to be within the West's sphere of influence given its colonial history, the threat posed by Cuban (and to some extent Chinese and Soviet) intervention on the continent seemed less imminent. That is of course not to say that the United States had no interests in Africa, nor was it unwilling to intervene when matters got out of hand, but Africa was (and is) generally fairly low priority for the United States. With some exceptions, Washington tended to defer to the former colonial authority, hoping that they would play custodian for Western interests. Africa was, to put it simply, a much safer bet for the Cubans. See Piero Gleijeses' Conflicting Missions or Visions of Freedom and Peter Schraeder's United States Foreign Policy toward Africa.