The Black Cats would only guarantee the Sky Sports pundit a position for the season.
Keane, 50, would have needed to shelve his lucrative TV deal to risk it all on gaining League One promotion.
The Irishman was not concerned about the drop in wages but there was no chance for him to plan ahead with the initial suggestion of a short-term stay.
In the end Alex Neil took the post on a reported one-year rolling contract.
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