2. There is no "sure-thing" head coach candidate out there
One of the hardest things to do in the NFL is find a competent head coach. If the New York Jets were to part ways with Robert Saleh, they'd have to embark on yet another coaching search. And while I'm not saying that Saleh is a great head coach; I think he's a fine one. He's not elite, but he's not among the worst.
And the Jets would risk not being able to find a competent head coach if they were to part ways with Saleh. This might not seem like a ringing endorsement of the coach, but it's just the truth. Plus, this team is stuck with Aaron Rodgers. They have invested a ton resources and even personnel moves in him.
Rodgers clearly views Saleh favorably, and if the Jets were to fire him, they risk upsetting Rodgers. I know that sounds ridiculous, but they dug themselves into this hole with the QB and now have to make it work. They brought in some of his former teammates and perhaps his favorite coach in Hackett, so why risk making him angry by firing Robert Saleh, someone he clearly gets along with and wants to play for?