Let them destroy each other. It’s so much fun to watch.
More room on the stage for each contestant, and allows for focused audiences. And just like the college rankings, the fans can argue about who made the cut just to get in, and which candidate is this year's Cinderella candidate. (no, that's not a Pete Buttiegieg joke, but it could be.)
Added bonus; the candidates could sell hats, shirts, key-rings, guacamole bowls, the list goes on.