Well, the refusal off the Americans to be completely clear is intended to deter any government in Taiwan from pushing the envelope too far and, for example, formally assert day jury independence, which which would trigger a Chinese military invasion.
美國人拒絕說清楚是為了阻止臺灣政府走得太遠,比如說,正式宣稱日軍獨立,這將引發中國的軍事入侵。