We've known for a while that Dwayne Johnson won't be appearing in Shazam! as the title character's long-time archnemesis Black Adam, even though the wrestler turned actor is still playing the villain in a standalone film at some point. But when Collider visited Warner Bros. to watch footage from Shazam!—you can find a rundown of all that here—director David F. Sandberg and producer Peter Safran sat down to discuss the film and, most notably, why exactly Mark Strong's Dr. Sivana was chosen over Black Adam for Billy Batson's first big bad. The …