Ever since The Passion made tons and tons and tons of money, Hollywood has been interested in the religious film market. Unfortunately, The Nativity Story wasn't the only attempt to attract a Passion-size audience that failed. But obviously the studios are going to keep on trying, because nobody wants to believe The Passion was a one-time occurrence.
I think that a lot of the interest in The Passion was in its controversy and its violence. I don't want to say that the movie made money because it was so bloody; I want to say that it had a great deal of publicity and media attention, partially because it was so bloody, and that it made money because people were curious about it. Sure, that doesn't explain the waves of church groups that rented out theaters for special screenings of the film, but maybe the church groups weren't the biggest contributors to the immense box office gross. If they were, where have they been since? And will they show up come Easter 2008 for the story of Mary?
More on Hollywood's religious crusades:
Fox Unveils Christian Division
Is Sony trying hard enough to reach Christians?
Passion of the Christ II -- Sort Of
New Line picks up Virgin Mary spec
A St. Paul (not MN) movie
Jesus is Back! (on DVD!)
Jim Caviezel Returns as Jesus