I don't know if this has been mentioned, I know there's a feeling that the challenges are pointless, but I love watching the games themselves. I agree that they don't do anything for the actual progress of finding out who the traitors are. Everyone has an incentive to do the best they can because they're all competing for the same pool of prize money earned.
I think of the traitors were actually banking the lost money from failed challenges and that's what they were competing for, it would actually make the discussions about paying attention to people's performance throughout the challenges make sense. That would incentivize the traitors to try and sabotage the challenges, or have to work hard against their own interest to avoid suspicion.
Just my thoughts.