Remember the "reality TV" show Who Wants to Be A Millionaire, hosted by Regis Philben? It always bugged me how it was marketed as reality TV. It's a fucking game show, we had those for decades before the term "reality TV" was coined. If this show is a reality show, so is fucking Jeopardy. All it is is answering trivia questions. Literally text book definition of game show.
Anyway, aside from that mini-rant, I think I figured out why it was such a huge hit at first and why people stopped caring so quickly. All game shows before it, the music was always light-hearted and cheery. But Who Wants to Be a Millionaire tried something different. The music was dramatic and tense. This dramatic music gave a false sense of suspense and had people on the edge of their seats for people's rambling trains of thought trying to arrive at an answer to a trivia question. This caused the popularity of the show to explode.
And I think the show ended up burning out, in part because of over-exposure, but also in part because people realized, "Hey, this isn't dramatic and suspenseful, just the music is."