I think because The United States allowed Japan to keep its emperor — Hirohito — after the war. Japan's post-war constitution became official on May 3, 1947, and Japanese citizens elected a new legislature. The U.S. and other allies signed a peace treaty in San Francisco formally ending the war in 1951.
According to Office Of The Historian," The outbreak of the Korean War in 1950 provided SCAP with just the opportunity it needed to address this problem, prompting some occupation officials to suggest that, “Korea came along and saved us.” After the UN entered the Korean War, Japan became the principal supply depot for UN forces. The conflict also placed Japan firmly within the confines of the U.S. defense perimeter in Asia, assuring the Japanese leadership that whatever the state of its military, no real threat would be made against Japanese soil."
Answer: Japan produced supplies for the United States during the Korean War.
