I imagine the NFLPA would have a mutiny on its hands if it agreed to that. This isn't like the NBA where the exceptions aren't position-specific. Imagine the union coming back to the players and saying, guess what, the quarterback can make as much money as he wants but the rest of you schlubs have to share a finite amount. Especially when quarterbacks generally have longer careers than anyone else because they're so protected.
I do agree 100% with you that players should have the opportunity to maximize their earnings and I will never hate on a guy who does that. Football careers are way too short. The guys I have no use for are the ones who clearly just don't want to be in Buffalo.