Two years ago, Peters was a solid player. Last year, pouting over his contract, he was mediocre at best (being generous). If the Bills cave and reup him for big bucks, who's to say he won't just turn into a giant pile of crap?
Through Stroud, the Bills showed Peters the way to bigger bucks. Work hard and you will be rewarded. I think that the Bills chances are better with a rookie 1st rounder at tackle than Peters, because you aren't sure which Peters will show up. If he's not motivated to play hard when he wants a fat contract, how motivated will he be after he gets a fat contract?