It's not even just the Bills, it's the new mentality for most teams. Look at Drew Brees in San Diego. He came in with high expectations, played like a rookie and they drafted another QB. Low and behold, his 3rd year of playing time he turned into a stud.
It takes time for most players to develop. It's rare that a QB comes to the NFL and doesn't struggle for the first couple years. But keep throwing them in the trash and starting over looking for the miracle QB....brilliant.