Four notes:
1) Peja does not pass the ball as a rule. He is not a bad passer when he chooses to. But he is essentially a "selfish" offensive player. I put that word in parenthesis because it is just his game -- he creates offense for himself, not others. But the fact remains, when he gets the ball his goal is to find a way to shoot it. Thus you can't run any offense through him until you are ready for the shot to go up.
2) Bibby normally only has the ball early in the possession. Then he hands it off to one of the big guys. From that point onward the offense normally runs through Webb or Miller, and Bibby himself is now basically a scorer.
3) Combine those two things and you have a situation where Bibby can't give Peja the ball very often at the beginning of the possession without the shot going up too early or the possession bogging down. And by the time it gets to the point in the possession where you would normally want Peja to have it, Bibby no longer has the ball in his hands except as a shooter.
4) Bibby is also not a drive and kick PG. He's primarily a shooter, with some sneaky ability to get to the hoop. But he rarely slices to the hoop and kicks out to somebody else on the perimeter. Which makes it tough for him to feed Peja. When our big guys work with Peja, they are inside and can kick it to Peja on the perimeter, or they can play a two man game with him and set a pick to pop Peja free. Bibby can't do any of that. In order for him to get the ball consistently to Peja given his size and position on the floor he'd have to be skipping the ball around the perimeter. Not our offense, nor a very good option.