Japan did not have much leverage at the time because it was highly reliant on the United States for its security, and the world at the time was much more polarized than it is now, regardless of the present troubles of this and recent years. Japan's domestic market alone did not provide the economies of scale, and it did not have a market for its exports of major tech aside from the United States, NATO allies in Europe, and to a lesser extent Korea, Southeast Asian, Latin American, and Middle Eastern countries. China was much less a factor to the global economy at the time... [Boy oh boy, how China has so thoroughly transformed itself from since the 70s and 80s...]
Pride is one of the main things that presently makes Japan not ditch its alliance with the United States for neutrality or indeed even a defacto alliance with China... Somehow, there are those in the LDP who still feel that China is inferior and that human resource wise and organizationally Japan is far better than China, even though many or most lament that the reality is no longer the case.
If I were Japan, I'd hint at that if the Americans were to go on and keep on testing me... But presently, the Americans are not antagonizing Japan, because they do not want Japan to turn on the US.
