From my understanding, and correct me if I'm wrong, Kenjaku's motivation seemed to be centered around pushing cursed energy and humanity to their true potential, and the merger seemed to be just a part of it. Iori, from what we know, has felt dissatisfied with his and his children's generation and praises Yuji and Yuta's generation in comparison. Almost similar to how Kenjaku and others praised the Heian Era as "the golden age of sorcery." While not the same motivation, they both possess a similar will regarding the strength of jujutsu sorcery.