I think this difference stems from how easy it is to apply and display your skills to projects outside of competitions. I mean, how are you going to demonstrate

I think this difference stems from how easy it is to apply and display your skills to projects outside of competitions. I mean, how are you going to demonstrate your mathematical problem solving skills to an employer in a side project? "I research the Collatz conjecture in my free time?" Contrast that with programming, where there are practical challenges abound whichever way you look. So those choosing to participate in competitions instead presumably have a much more narrow range of motivations. I can't tell you why this should translate into dismissing these people, but there is certainly a difference.