User blog comment:Hyperborean/"The House of Hades" – official expectations blog/@comment-8848260-20131003231046/@comment-8848260-20131004012922

matt5858 - I would suspect that it was because it was the first time (?) his books were optioned for a film and that would be exciting for anybody. It also helps the sales of books even if they were successful beforehand. The Lightning Thief flourished and expanded it's fanbase following the first movie. Film adaptations promote the books to audiences that have never heard of it (or weren't interested before seeing the movie).