Because the trailer for "I'm So Excited" doesn't reveal anything at all about the movie.
Oh, sure, there are a couple of hints. For instance, we know the title, which is reinforced by the Pointer Sisters hit "I'm So Excited" playing throughout. Also, we know it's by Oscar winning director Almodovar ("Volver," "Talk to Her"), because it says so right on the screen. And there's something about an airplane and dancing flight attendants.
Otherwise, well, you got us. This is either some kind of outre European comedy or the cleverest viral ad campaign in the history of Old Navy. "I'm So Excited" doesn't yet have release date here in the U.S. but you can check out this odd little music video right now if you want, courtesy of Apple Trailers: