I believe Mayfield is going into his last contract year. Cleveland just spent $230mil on Watson. That's not "backup" money, so he feels like Cleveland's moving on from him.
I think Mayfield's a punk, but this looks like another reason why Cleveland gets high draft picks. They're chronically mismanaged. Baker's an above average QB. Not great, but serviceable with an NFL quality offense. Cleveland was on the verge of fielding one, but now they're jettisoning another top draft choice for a flashy, expensive piece of a puzzle that was already filled. Much like Dallas did with Jerry Jones and Barry Switzer, they bring in the big, high-dollar names, but don't understand the role level players that actually make a team function.