為什麼美國海軍預測颱風輸給了日本?是哪一方面的技術性層面?

The main reason is Joint Typhoon Warning Center (JTWC) is not a meteorology institution.

JTWC's primary responsibility is to assist U.S. Navy's operation in the Pacific, while sharing information to other institutions. The U.S. official meteorology institution remains as National Weather Service, National Oceanic and Atmospheric Administration.

Because JTWC is a military unit rather than civilian government agency, its personnel turnover rate is expected to be higher. Hence, the average experience of its personnel, even with the same education, is less than its counterpart government employees.