Some team has to set the precedent and just let their quarterback go, rather than just being next in line to set the top of the market. Maybe that's Belichick and the Patriots who said goodbye to the GOAT and just signed Newton for next to nothing? New England has always done their own thing and have made unconventional decisions work in the past.
Quarterback salaries are already well out of hand and it's just a matter of time before a team realizes it and just lets their guy walk.
It's already happened with the Redskins, they let Cousins walk and it blew up in their face.
It's just too hard to find a good QB.
Granted they could've gotten lucky and found one, but that's the point. If you already have a good one, pay him and you don't need luck.
There is of course a threshold where the QB becomes so expensive that it prevents fielding a competent team, but I don't think we've reached that point yet.