They want to fight, they just don't want to risk losing.
Based on tonight's performance, I suspect Fury would be wary of fighting Usyk, even though he was spouting off about December - to which Usyk agreed.
As you say, though, Usyk is the only one prepared to take a chance and, unless Fury can get himself in to shape - I thought he looked out of condition tonight - I can't see the fight going ahead.