Here's why:
* "Banned" is a broad term: A book might be removed from a school library, challenged in a community, or restricted in certain settings, but not technically banned nationwide.
* Data collection is inconsistent: There isn't a central authority that tracks all book banning instances. Different organizations collect data, using varying definitions and methods.
* Bans can be temporary: A book might be challenged, but then reinstated after public discussion.
Organizations that track book challenges and bans:
* PEN America: Provides data on book bans in schools across the US, focusing on recent trends.
* American Library Association (ALA): Collects data on books challenged or banned in libraries, but doesn't track every instance.
* The National Coalition Against Censorship (NCAC): Monitors censorship efforts in various forms, including book banning.
While exact numbers are difficult to pin down, the organizations mentioned above provide valuable insights into the prevalence of book banning in the US.