In the last 4 years the Bears have played 5 QBs, Collins (oof!), Haine, McCown, Campbell, and the starter Cutler. Whenever someone other than Cutler has been at QB the Bears have played worse than with him. While this can be dismissed as "those guys are all back-ups" it should also be considered that the Bears traded away Orton, who was having a problem with not being able to go through his reads, find the open man, and throw it before the defensive rush got to him. This was because Orton needed at least 2.5 seconds to do these things, and most pass rushes were getting to him in 2.0 to 2.2 seconds (in one case a team was able to get to Orton in 1.8 seconds). (NOTE: only Ortons' last season is valid for comparison due to different players during Ortons' earlier seasons versus Cutlers' first season.) The fact is Cutler has been able to win, where other QBs have lost. This is with the same OL, and the same WRs, and the same RB. Who was it that said that "Great players elevate the (game)play of the players around them"?
Next, there is the OL itself. As poorly ranked as this O-Line has been, how likely is any other QB going to do well? Yes, there are QBs coming out of college who are able to transform a team, however, it stands to reason that there are more of them that can do it from behind an O-Line that can protect well. Not improving the O-Line means that bad QB play must be solely on the QB, therefore, if the QB is unable to perform, an new QB is needed. This forces the team to find a great, mobile and/or hard to tackle QB, instead of only having to find a great QB. This reduces a teams chances of finding a great QB for this team considerably. I would think the reduction would be between 50 and 90% While the percentages are my opinion, the basic logic is difficult to dispute.
Now it is possible that the O-line will be dramatically improved by new coaching, scheme, the addition of new talent, and the physical recovery of some players, but I've heard that before. The reality is that a improved O-line is not guaranteed. Further, Emery/Trestman have to plan not just for next season, but seasons beyond as well. I will not assume that all of the problems on the O-Line will be "fixed" in a single off season. It is more likely that it will take AT LEAST 2 seasons, more if things go poorly. The Bears know that the team can be successful with Cutler behind a bad O-Line. The alternative is for the Bears roll the dice on a "new" QB while building the O-Line, and this just leads us back to where we are. Is it the QB? The O-Line? Both? Who knows? And the circle of blame and the lack of accountability continue... Nope, not where I want to be if I'm a team, coach, or GM. Bottom line here is that Cutler is (at a bare minimum) a known quantity, and it will be easier to gauge the O-Lines progress with the same QB.
Further, keeping Cutler establishes a bar for his replacement. If a player wants to be the starting QB, he has to be better than Cutler. The beautiful thing about this idea is that if you are a member of the "Jay Cutler Sucks!" crowd, then this would mean that the bar is set rather low, and soon, some UDFA, or, some late round draft pick that was cut by another team that the Bears signed, will be taking over the starting QB spot in just a year or two, and Jay will be Cut (ba-doom-tish) from the team. If you are in the "Jay is a Great QB!" crowd then Jay will be here for some time to come. This is a competitive concept, may the best man win.
As an added benefit, Cutler will have been signed when his value is low, rather than paying for his peak performance with the expectation that said peak performance will be maintained.