Money
It’s hard to see Christopher Johnson having any desire to pay two head coaches at once.
If the Jets fired Gase at season’s end, they’d be on the hook for the rest of his contract. After firing Todd Bowles and Mike Maccagnan, New York would have to pay those two, Gase, the new head coach and Joe Douglas. That’s not a situation that seems to be appealing to any owner, let alone Johnson.