Sukuna has been around for thousands of years...There's not much that entertains or bothers him anymore, nothing interesting ever happens so he remains bored as he lies borderline dormant in Itadori's body...You are something new...

He can't tell what you are but he didn't care because when you separated him from Itadori just to bind him to you to keep him tame, he was hooked...You're so powerful and you smell so very sweet...Maybe he'll keep you as a pet after he breaks out of your hold...