I think part of that is that a Bears loss exposes, or reiterates the common assumption that they are paper leader right now. If they lose to GB then the assumption is they will lose again next time they play at home, because GB is supposed to be better and they would have proved it on the field.
The football world expects Chicago to fall on its face, and maybe sneak in as a wild card before getting stomped in round one. If they beat GB, that expectation will be mostly thrown out the window