The movie was originally intended to be a direct-to-video release, but Warner Bros. decided to release it in theaters. The problem wasn't the film itself: it was very well-received by critics for its animation style, dialogue and voice acting and many claim it's just as good if not slightly better than Christopher Nolan's Dark Knight trilogy.
The problem was Warner Bros. released it on a very short notice with almost no marketing campaign for it. For it to be a hit, you're going to have to have the execs launch a bigger marketing campaign.