As for the reasons of his dismissal, it is said that he neglected the administrative affairs addicting himself to alcohol and women; he was a Christian; and it might have been a result of the Shogunate's policy to abolish powerful non-Tokugawa feudal lords, because the Tsutsui clan was one of such lords even ruling an important area of Kinai region (including five powerful provinces near to Kyoto).
改易の理由は、定次が酒色に溺れて政務を顧みなかったこと、キリシタンであったことなどのほかに、筒井氏のような外様大名を畿内に置いておくのは危険と考えた幕府の有力外様大名取り潰し政策の一環とも伝えられている。