Lack of source material: The Vampire Knight manga was still ongoing when the anime was produced. The anime caught up to the manga, and there was not enough material to continue the series.
Commercial performance: The Vampire Knight anime did not perform as well as expected in terms of sales and ratings. The cost of producing a third season would not have been justified by the potential revenue.
Creative differences: There were some creative differences between the author of the manga and the production team of the anime. These differences led to disputes that eventually resulted in the discontinuation of the anime.
Despite these reasons, Vampire Knight remains a popular series among fans. There have been several spin-off manga series and video games, and the series continues to be enjoyed by readers and viewers around the world.