Why do the hosts give such a detailed synopsis of the next movie they're introducing? A little backstory, some interesting facts about the performers, or the production, or the studios, or the public's reaction, fine. I wouldn't mind a word or two about the movie, a thumbnail view, it's just that they practically tell me everything I'm about to see onscreen, which to me defeats the purpose of watching the movie! If I wanted someone to tell me what's about to happen before it happens, I wouldn't be watching it.
I always hit the mute button when they start their spiels, and once the opening credits roll, I turn the volume back up.
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I think it's just that they (TCM, its employees and subsidiaries) are such authorities and pundits of the medium of film, especially classic film. Think of it the same way as a college professor explaining a master work of art. They present facts about the artist, the model (if relevant), the era, the media, the technique, the application and any social or political impacts that may have affected the art or that the art may have affected.