People were questioning Lamar because he had spent 3 years regressing and ended the last 2 early with injury. Those are red flags and people were right to raise them because they are issues that matter.
However lets talk Fields for a second. Lets talk about every team in the NFL right and look for ones who you could argue would bring him in to start. In the AFC you have Denver, who are in a full rebuild the next 2 years so are not going to be looking to get a QB for 1 year anyway, the Steelers, who are taking their shot with Wilson, and the Raiders but I am not sure he could beat out Minshew (yes he has been that bad). In the NFC you have just the Vikings but, aside from the fact that I do not think he can beat out Darnold, everyone knows from their trade earlier what they are looking to do in the draft so the QB position is about to be fully occupied.
Fields fundamentally does not have good enough mechanics to be a starter in the NFL. The entire rest of the NFL realizes this and are not pulling the trigger on him to start which means any trade for him is going to probably be a day 3 pick and the Bears have to make peace with that.