According to the search results, Sukuna forcefully escaped from Yuji Itadoris body and attempted to take over Megumi Fushiguros body because he needed a new vessel and believed Megumis powers made him a suitable candidate. Sukuna saw Megumis weakened state as the perfect opportunity to take over Megumi as he had been intrigued by the latters shadow techniques from the beginning of the series. Sukuna took control of Megumis body after defeating and killing Tsumiki and Yorozu. Although Sukuna managed to leave Yujis body and get into Megumis body, he didnt have full control over the new vessel yet. Megumis consciousness frantically fought Sukuna from taking over completely. Since Megumis spirit was broken by seeing his sister possessed by another ancient sorcerer, Sukuna has complete control over him, unlike with Itadori. The latest Jujutsu Kaisen manga chapter revealed that Sukuna is gaining even more power and control over Megumi as he falls more into the darkness, and it seems impossible that Megumi will be able to break free on his own.