Shizuma himself did not attack he only defended himself, in one of those that cornered him he saw something similar in what he saw in Nezuko (since a few days had passed since Nezuko had become a demon and helped Tanjiro) where he could not kill him at that moment.

but when he tried to get close enough, one of his horns broke, making it more difficult to probe Shigaraki's mind. Just a few days before, Aizawa found out about his existence, that he is his son, and at that moment, seeing him like that in front of Shigaraki, he became very frustrated.

the war. Keane himself didn't care much because of the appreciation he had for being the brother he always wanted.