With the caveat that everything I'm about to suggest is in theory and not yet proven, the Browns have literally done everything humanly possible to eliminate everything that went wrong last year that was out of Baker Mayfield's control.
Offensive coordinator had such a dysfunctional relationship with the head coach that it caused play calls to get in so slowly that audibles and presnap reads really couldn't be made? He's fired.
Quarterback coach had no experience in the role and couldn't provide in any actual coaching when things got tough? He's fired.
Head coach was insecure and incompetent? Both with his game management and his playcalling? He's fired.
General manager was forcing head coach to play certain players over others even if they weren't as good? He's fired.
Both starting tackles are terrible? They're both replaced by a top 10 draft pick and a free agent making 30M GTD.
Tight end room isn't that strong? Added the highest paid TE in the NFL and a draft pick who some people thought was TE1.
On paper there's no excuses for Mayfield. The Browns addressed every single issue offensively that was out of Baker's control. Simply put, it's up to Mayfield to play better.