Here's why:
* LC call numbers are a system used by the Library of Congress. They are primarily used in libraries that subscribe to the Library of Congress cataloging.
* Other libraries use different systems. Some libraries use the Dewey Decimal System, while others have their own unique call number systems.
* Not all books are cataloged. Some books, especially very old or rare ones, might not be cataloged in any library.
* Some books are not published. For example, unpublished manuscripts or privately printed works might not have a formal call number.
Therefore, while LC call numbers are common for many books in large libraries, it's not accurate to say that all books have them.