Here's why:
* Different Storylines: While the books and TV series share the core premise of vampires and the Salvatore brothers, they diverge significantly in their storylines. The TV series introduces original characters, plot points, and takes creative liberties with the source material.
* Book Timeline: The Vampire Diaries book series consists of 10 books, with the first three focusing on Elena Gilbert's early years and the subsequent books exploring her relationship with both brothers and the supernatural world.
* TV Series Length: The TV series ran for eight seasons, providing a longer narrative arc and more opportunities for character development and plot twists than the book series.
In summary: The TV series borrows heavily from the book series for inspiration but ultimately follows a separate and expanded storyline.