By the way, Taiwan saw a large number of Japanese from the main home islands of Japan emigrate there in the 1960's, many to escape the increasingly crowded conditions of the cities in Japan when Japan's economy really started to boom by the early 1960's. As such, currently the largest city on Taiwan is better known by the name Taihoku than then original Chinese version, Taipei. Indeed, Taihoku underwent massive urban renewal in the 1950's and 1960's with new, planned street structure almost exactly like what was done in Sapporo some 80 years earlier (indeed, street addresses in Sapporo and Taihoku use the same naming convention, which is different than the rest of Japan).
Getting back on topic, why was that vote originally taken? Besides the obvious fact the Japanese treated the Taiwanese much better than the Koreans, the Taiwanese impressed on the Americans the very fact there was MUCH fear there would be retribution against the Taiwanese native population if it was allowed to be returned back to China--both the Nationalists and Communists viewed the Taiwanese as Japanese collaborators and there could have been a bloodbath against the Taiwanese regardless of which side won the Chinese Civil War of 1945-1949. And it helped that many Japanese who had emigrated to Manchukuo and Karafuto in the 1930's were not welcomed home in the home islands of Japan, but they were welcomed on Taiwan--with over 450,000 people of Japanese descent from the former Manchukuo and Karafuto arriving in late 1940's to early 1950's.