It's not a single move. It is a single factor. Rex's inability to identify, hire, and develop young coaching talent. It's been 4 years. Are their any coaches he has hired that were any good other than Karl Dunbar who was already a great D line coach before he was hired. Plus, Rex keeps incompetent coaches way past their expiration date. See schotty and cavanaugh. The problem is masked on D where Rex is the defacto D coordinator but he relies on Sutton ( a holdover from previous jet staffs) and Thurmon (brought over from Baltimore).
This, IMO, will be the main reason Rex is eventually fired. Coaches who can't groom young assistants have a short shelf life.