In the span of 2011-12, 10 QB's were drafted and are starting for their respective teams. Aside from Newton and Luck, the Bills had a chance at all of them. It is inconceivable that those other 8 did not have what Nix was looking for.
You do not wait for the draft to come to you and expect to find a veritable starting QB. If you state that repeatedly, sure, you'll never get the guy.
There are several NFL teams that must rebuild from a failed regime and almost none of them do so without getting their QB near the beginning. 10 teams have done it and while it does not guarantee success, it remains the responsibility of the GM to get that guy ASAP. RF was not their choice upon taking over, had 2 years of film (08-09) that showed he's not a franchise guy, and they still went with him.
Nix's teams are 13-27 in 2+ seasons. So now, they'll grab their guy when it's abundantly clear they need one which provides them another excuse why this rebuild needs more time.