When one is reading the myths it is easy to ask, “Why would the Yamato choose these myths?”
The reason is three fold. One, the myths were already well disseminated throughout the Yamato Empire. The names Amaterasu and others dominated the emerging Shinto legends.
Two, when Prince Toneri in the eighth century had the legends put into written form in the “Kojiki” and “Nihon Shoki” to impress the Chinese; they both demonstrated Japan, or the Land of Wa, had a viable culture and emerging civilization.
Finally, the Chinese were already familiar with Kyushu and Hyuga. They lie closer to China than the main island Honshu does. It stands to reason that many in the Han Court were already familiar with the myths.
The Yamato, like all conquering people, saw a culture of legend that they were lacking. The Yamato were more concerned with centralizing power and conquering the other tribes of Japan. Kyushu being so far away and the descriptions the Yamato warriors brought back fueled an idea of an exotic land where gods and goddesses roamed and Japan’s first Emperor would have surely been proud to claim the land as his own birth-right and seat of power.
Much as was done in our Western tradition when the Israelites conquered and incorporated into their myths those of the vanquished. Much as Rome took the Grecian Pantheon and made it Roman. The Yamato simply took the pantheon of Kumaso, Hayato, and other tribal gods and made the gods their own.
As Tolstoy noted, “History is written by the victor. The vanquished concede all, including their culture.”