Cutler did not do very much more with each passing attempt than Edwards. When you look at stats that keep the subjects on level ground despite discrepancies in passing attempts, you see they didn't wind up too far apart. My favorite stats for QBs are yards per attempt, completion percentage and TD/INT ratio. Now I planned on coming in here and ranting on why Cutler is far and away better than Edwards, using those stats as the basis for my argument...but IMO, there just isn't much of a case to be made there. If you take a look at those stats, I think you'll be surprised. I know I was.
If I'm starting a brand new franchise, Cutler is my guy. But, because they don't seem to be very far apart at this point, Edwards already having been here for a couple of years means that giving up resources to make the swap happen just doesn't seem to make a whole lot of sense.