His nick name if “One Take Probst” and that is part of the reason. Also, they strive to get everything on the first take to keep it as “live” as possible. It’s one of the few shows that does not rely on recorded narration to describe the rules of the challenges. Probst gets those right on the first take usually and they just air his explanation to the contestants on TV.
I’m too lazy to look for the quote, but Probst commented on this some seasons ago. The way he and Burnett envision the show, they very much want to play into the “tribal” aspects of the milieu. So while it’s not exactly a sacred ritual, the concept of those little moments being ritualized by specific repetition, and therefore set in stone, is part and parcel of the producers’ intent.