He’s not. Elon already offered him the position and he turned it down.
My guess is that Jack rolled some shares into the deal to keep the option of being the rescue CEO in play. But not to be Elon's boy. If the banks end up owning Twitter, they will need a CEO.
Jack isn't stupid. Twitter was a losing battle, albeit a slow one, right now it is a sinking ship and the job description is essentially 'who wants to ride this down'. Dorsey doesn't need the money anyway.