What Killed The Movie Trailer?

Movie Trailers may have started out as a tool to sell films, but over time they have evolved into their own spectacle. Before a film is released there are a multitude of Theatrical Trailers, TV Spots, Web Shorts, and even Trailers before the Trailer starts. How did Hollywood turn from a simple marketing tool, to a an ever expansive industry of movie trailers that mostly give away the entire plot of the film? How did Hollywood crush the Movie Trailer?