User blog comment:The Mighty Thor/BATMAN 3!!! YOU GOTTA GET YOUR ACT TOGETHER!!!/@comment-3361105-20120615211201

I think they're just trying to keep their cards as close to their chests as possible, in order to keep the story fresh and exciting. With the Avengers, you knew exactly what you were going to get - big lugs punching each other and wise-cracking. With Batman, it's a game of wits, and to ruin any of the cool things in the movie with the trailer would decrease the impact of the movie as a whole.