Ultimately this is a question for the people and governments of these countries if they want to be open to visitors. And I think you are missing a big factor international relations and security. The more intertwined with the global community on every level the more secure and stable a country is. People in the US and Europe will care little about a country they have never heard of halfway around the world but you better not mess with the places they take their winter vacations or get their bananas.