Stafford's Deal Seemed Fair To Me

I understand the thoughts on Goff and Gurley signing too early (see what I did there?), but Stafford played out his last year of the deal in the Super Bowl season ($23mm, which is under what he could have received) then signed a 4 yr./$160mm deal; $40m/year.

All QB's since have been over that on an annual basis. I know he was injured last year and has a lot of wear and tear after 14 years, but I do not get that people thought he "should" have signed for?