2. The Avengers 2 Is Released The Same (Rumoured) Year
Admittedly, this reason is quite flimsy since there isnt a concrete release year for Justice League, but its rumoured (and listed on IMDB) as a 2015 release date - or in other words, the same release date The Avengers 2 is set to come out. This shouldnt really be a massive problem because a lot of people will no doubt go and see both movies if theyre both well reviewed. However, your part-time movie goer who goes to the cinema once every month or two isnt going to go out of his way to see two films and, based off how good The Avengers was, theyre more likely to go with a safe bet and stick with characters they already know than go into a whole new story and characters. The release dates will probably be widely separated, just as The Avengers and The Dark Knight Rises was this year, no doubt Marvel didnt want to fall into TDKRs summer black hole. However, on the off-chance that the two films release at a similar time, this could be fatal for Justice Leagues success.