Do you remember when movie trailers were called previews? I sure do. And I don't understand why we made the switch. "Preview" makes much more sense since it is, indeed, a pre view of a movie. And trailers don't follow behind movies, so why call them that?
By doing a little investigation (which means I looked it up on Wikipedia) I learned that ads for new movies did originally follow the main feature. But this practice didn't last long since most movie patrons left the theater before the trailers were over.
But even after they began being shown before the movie, they were still called trailers - by the movie industry. I think it's just us peasants who called them previews. Or if we were being really formal we might have referred to them as the "coming attractions. "
Now everyone uses the term trailer, which I think is too bad. But, whatever they're called, I enjoy them. And I love that you can find so many of them on You Tube these days. Here's one of my favorites: