Of course, it is possible that the studio was trying to get the release out as quickly as possible, and forgot to include the executive producers. However, it is also possible that Christopher Nolan, who directed the highly-successful trilogy Batman Begins, The Dark Knight and The Dark Knight Rises, didn't agree with the casting choice and left the project.
After all, both Christopher Nolan and Emma Thomas were listed as executive producers in the studio's Comic-Con 2013 press release where they announced Superman and Batman will be featured in director Zack Snyder's sequel. And its been confirmed that Ben Affleck was in talks way before Comic-Con even happened.
If Christopher Nolan and Emma Thomas did leave the project because of Ben Affleck's casting, they wouldn't be the first to express their distaste of the new Batman. We reported last week that over 30 online petitions were launched to try and get Warner Bros. to remove Ben Affleck from the role.
Christopher Nolan and Emma Thomas are currently in production on Interstellar, which is set for release on November 7, 2014.
Batman v Superman: Dawn of Justice comes to theaters March 25th, 2016 and stars Henry Cavill, Ben Affleck, Amy Adams, Diane Lane, Laurence Fishburne, Gal Gadot, Jesse Eisenberg, Jeremy Irons. The film is directed by Zack Snyder.