Final answer:
Arab traders brought Islam to the island nations of southern Africa hundreds of years ago.
Step-by-step explanation:
The reason why there are more Muslims in the island nations of southern Africa than the mainland countries is because Arab traders brought Islam to the islands hundreds of years ago. These traders, who were conducting trade along the Indian Ocean coast, spread the Islamic faith to the island communities. The geographic isolation of the island nations also contributed to the preservation and growth of Islam in these areas.
Learn more about Islam in island nations of southern Africa