It’s that their shot at glory. The pinnacle of their sport, and the crowning achievement of their entire career happens once. In their lifetime for most of them.
Brady and jordan never experienced that pressure. Where they had one shot and one shot only to secure their legacy. Not a whole game of competition, or a series where you can have a bad throw, or a series of game where you can have a bad game. You have to be clutch every single time on the beam.
Not to mention the danger of losing focus on the beam exceeds the dangers of QB1 losing focus.