Here's why:
* Massive sales: The series has sold over 500 million copies globally, making it one of the best-selling book series of all time.
* Movie franchise: The eight Harry Potter films have grossed over $9 billion at the box office worldwide.
* Merchandise: The books have spawned an extensive range of merchandise, including toys, games, clothing, and more, generating significant revenue.
* Theme parks: The Wizarding World of Harry Potter theme parks at Universal Studios have attracted millions of visitors and contributed substantially to the franchise's overall earnings.
* Other ventures: The Harry Potter franchise has extended to stage productions, mobile games, and other ventures, further adding to its financial success.
Considering the immense popularity and diverse revenue streams, it's evident that the Harry Potter books have been a financial behemoth, generating billions of dollars in revenue across the globe.