Lionsgate just sent out a press release that said the trailer only contained footage from the first half of the movie (obviously to all the fans, lol.) They say:
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In an attempt to preserve the anticipation and mystery that fans are relishing, the trailer only shows footage from the first half of the film, chronicling events leading up to but not including the Games themselves. After giving fans their first look at all of the book’s beloved characters brought to life, giving viewers who haven’t read the book vital information about the world of Panem, the trailer ends with an electrifying cliffhanger right as Katniss enters the arena.