Sometimes they don't. Geno is who I thought he was. It's all in the mindset. When the system breaks down, he does too.
I have a few points in response, but I want to note that I understand your viewpoint and cannot say that its false.
Firstly, I think the majority of quarterbacks are the same way with respect to breaking down in chaos. I don't think a single quarterback in the league currently actually excels when the system breaks down. In fact, I think the best quarterbacks are so system-dependent that they define their own style of system. Brady, Manning, etc. all became synonymous with the systems they excelled in and therefore facilitated.
Sure, some quarterbacks are better outside of play structure than Geno, especially those adept at an improv-style of play like Mahomes. But to me, that's stylistic, and again, a lot the best quarterbacks of all time were kinda the same way. The Bradys and Mannings of the world also didn't do well with the improv stuff. Not to compare Geno to Brady, which some will accuse me of. It's a little like saying every girl is either a Marilyn (Monroe) or a Jackie (Kennedy). Just talking about archetypes, not making a comparison.
Secondly, I think Geno Smith's crumbling is usually a little bit overstated. I think people have it in their head that he's going to crumble under pressure and they try to fit any adversity he faces into that "he's folding under the pressure" box.
I don't think Geno did fold, though. I think he made some stupid mistakes under duress, but I think he responsed. I don't think he broke.
I think Geno has more mental fortitude than he's credited for. I think he's proven it a bunch by winning us games that he could've lost us in crucial final drives.
Geno had a bad, bad day yesterday. I don't think it changes my perception of the past 2 years of which I saw a competent quarterback with a natural arm, an insane story, and a team who responded well to him.
This type of thing was always going to happen at some point. He hasn't been protected at all and faced instant-pressure more than any quarterback in the league last week yet again. I'm not saying that absolves him of the responsibility for his mistakes, but I don't think it's especially possible for a quarterback to be consistent in these circumstances.
Of course, most won't read this due to its length and will insult my intelligence and objectivity without reading the points I've made, so that's discouraging. I appreciate you though,
@pittpnthrs - you give me proper consideration despite the disagreements.