Every single initial trailer for every single Pokemon movie ever made? This isn't something new and different. The movie isn't done yet, so they're just creating some quick footage representing it to use in the trailer instead of being forced to 100% finish very specific parts of the movie extremely early just so they can make the trailer by a particular date.
So why even make these footages for the trailers if it's not going to be in the movie? Trailers are supposed to advertise a film with footages that will be exhibited in the final product. Why not use actual footages in development for the trailers?