Huh what a coincidence I just watched this video https://www.youtube.com/watch?v=a_jjzzgLARQ which covers the trailer industry. Pretty eye opening to see all the tricks behind the trailers, a almost-must watch.
I think people are watching movie trailers because they're almost self-contained movies. Very frequently the protagonist and antagonist are set-up, the protagonist's challenges are laid out, the protagonist is shown overcoming the challenges, the nature of the twist is shown (and sometimes the twist itself is hinted at), any romantic relationship of significance is both shown and shows the direction it will go in the movie, half the big awesome SFX scenes are included, half the funny one-liners are included, and every character of significance is revealed.
Sometimes you literally don't even need to watch the movie, you just got the tl;dw in the trailer.
I refuse to watch trailers for movies I might see, because they ruin the experience since I know everything that's coming.
