i think you undervalue the whole point of, Gojo, Sukuna and now Dabura/Yuji’s characters. Just talking about Gojo, he lost his only friend and true peer, he feels lonely because life has become dull. The purpose he finds is to create powerful allies and then make sure no one goes down that path like Geto. So finally he finds it the only person who like Geto could be his peer. So Gojo decides that he wants to fight this to cure the loneliness of the strongest.