Here's why:
* Access Restriction: The game restricts access to certain areas until specific tasks are completed or certain items are obtained. This keeps players on a set path and prevents them from progressing too quickly.
* Puzzle Element: The library annex contains a hidden passage that leads to the Chamber of Secrets, but it's initially inaccessible. The game requires you to solve the riddle of the talking bust in the main library to gain access.
* Storytelling: The locking of the annex is a way to build tension and curiosity. It makes players wonder why it's locked and what secrets lie within. This reinforces the mysterious nature of the Chamber of Secrets and the danger that lurks within.
In short, the locked annex is a deliberate design choice by the game developers to create a more engaging and challenging experience for players. It's a puzzle that needs to be solved before players can progress further in the story and uncover the secrets of the Chamber of Secrets.