The reason for this is that he let his opportunity for taking the reins of the government go by, although it was an absolute chance to do so if he had gone to the capital (Kyoto City) when Yoshiaki ASHIKAGA was in exile.
その理由として、足利義昭が亡命してきたときに上洛すれば天下を取れる絶好の機会であったのに、それをみすみす逃がした。