As a defeated country in World War II, why did Ryukyu occupied by Japan become Japanese territory instead?

Ryukyu used to be a vassal state of China.

Later, it was occupied and colonized by Japan and changed to Okinawa Prefecture.

After Japan's defeat, the United States intended to return Ryukyu to China on condition that Chiang Kai-shek sent the ace troops trained by Americans in northern Myanmar and western Yunnan to Japan. But Chiang Kai-shek wanted to use this unit to fight the civil war, so he refused. After that, Okinawa did not give it to any party for a long time. Only managed by Japan. Just a few years ago, the United States returned to the Asia-Pacific region, thinking that China was the biggest threat to the United States in Asia, and Okinawa was nominally given to the Japanese. In fact, Ryukyu people have fought for independence there many times. Of course, they are mainly aimed at Japan's failure to handle the issue of US military presence.