Actually US have been pressing Japan to gear up and throw out the article 9 since the 80s. Japan avoided it by putting the burden of defense on US while they grew economically. As a concession they pledged monitory support to US military adventures in the form of human development aid in Iraq & AF and also in the 1st gulf war. The US bases and soldiers in Japan are financed by Japanese gov. Infact US did allow Japan the right to reprocess spent fuel and under a agreement in 86 & as per experts Japan may be able to go for nukes without much legal repercussions. While US allies such a S.korea doesn't have such privileges. US wants a militarily stronger Japan under their wing.