To me it is a question of value. To get a 33 year old Stafford in March you'd have to send a couple of draft picks to the Lions and then also pay him at the very least 20m in salary on a 2 year deal. The entire deal to get him here is just too expensive for my taste. If he'd be cut -- which he won't be -- and you'd get him without any draft picks it would be a different story.
As much as many don't like to hear it but to me the most likely scenario going into next year is still Newton, Stidham, rookie QB. That is if Cam agrees to a team friendly deal. I get why a lot don't like the option as they want a more traditional QB who throws the ball more but at the same time I can see BB continuing to be fascinated by all the oldschool stuff he could pull out especially with a full offseason to prepare.
I would have loved to see Mariota work with McDaniels but I think he might be the starter for the Raiders next season. Carr might be among the best among potentially available QBs next offseason and he'd most probably require the same package as Stafford (assets + ~20m APY).
Either way it will be an interesting offseason..