The Indian Ocean trade routes were already known to him and to other Chinese sailors. He visited Africa, India, and the Middle East, and in a way, his journeys were trade missions, but not in the sense of filling his ships up with stuff to be sold later for higher prices. At the time, China was the leading manufacturer of quality goods in the world, and there wasn't anything they actually needed to import. What they needed was prestige and respect so that people would continue to see China as the center of the economic universe. So there was a tribute system, through which foreign rulers or their ambassadors would come to China and engage in a debasing ritual called the kowtow, wherein they acknowledged the superiority of the Chinese emperor and offered him, or her, but usually him, gifts in exchange for the right to trade with China. The opportunity to humble yourself before the Chinese emperor was so valuable that many a prince was happy to jump on a treasure ship and sail back to China with Jung Ha. Also, these tribute missions brought lots of crazy things to China, including exotic animals.