Any kind of "contest" - a TV quiz show, a football match, a baking competition, the darts or who has the best b'n'b - only makes sense if the contestants can affect the outcome through their own efforts and abilities.
Different contests demand different skills: general knowledge or perfecting a physical skill or cleaning a toilet correctly. It doesn't really matter.
(Then, you can even have deconstructed/absurdist contests (like Shooting Stars) where the absence of any connection between effort and outcome is the joke.)
Of course, the contest element is only the scaffolding on which the show or event is built. I guess I watch to see how luck and personality and circumstance has a bearing on the outcome, and how different people cope to win within the framework of the contest. There is a reason why coverage of the darts has a split screen so you see the player's face as well as the dartboard.
And then there are layers of tone. I watch Taskmaster because it's funny, Four In A Bed because it's cringey, Match of the Day because it's elite sport. But all of them share the basic rule that the players of the game affect the outcome through their efforts and abilities. If the contest is random then the format is redundant.
Traitors is like watching a football match where the teams play for 90 minutes then someone draws the winner out of a hat.