I may be giving Stephen King a copout here but I interpretted the surface level personalities, mundane conversations, and therefore mediocre dialogue as essential to the story. The contest features a bunch of teenage rejects who entered into a ridiculously unfavorable suicide mission - there shouldn't be the brightest and most clever people involved; it's a bunch of hopeless lunatics trying to distract themselves from thinking about their impending doom.

I'm with you though, I almost gave up at that exact same area in the book. While I did think the dialogue improved a bit as people got more desperate, I'd moreso say I just got more attached to my own preconceived view of the dialogue.