The official reason from Warner Bros. is
"to give the filmmakers time to realize fully their vision, given the complex visual nature of the story. The decision was made following the shift of the start of production to second quarter of this year."The sequel to Man Of Steel sees Zack Snyder return as Director, along with Henry Cavill as Superman, Amy Adams as Lois Lane. Amongst the newcomers joining them will be Ben Affleck as Batman, Gal Gadot as Wonder Woman and possibly a whole host of other DC Comics characters.
More news as we know it.
