Here's why:
* The Fairy Godmother's Magic: The entire transformation is explicitly attributed to the Fairy Godmother's magic. This is a well-established element of the fairy tale genre, where magic is expected and accepted as part of the narrative.
* The Time Limit: The Fairy Godmother clearly warns Cinderella that the magic will wear off at the stroke of midnight. This sets up the expectation of a reversal, and the reader is prepared for the transformation back to its original state.
* Symbolic Significance: The transformation serves as a powerful symbol of the ephemeral nature of Cinderella's dreams and the harsh reality of her life. It reinforces the Cinderella's humble beginnings and her eventual return to her impoverished existence.
In essence, the reader isn't surprised by the transformation because it's a crucial plot point that plays into the story's themes and serves as a reminder of the limitations of magic and the importance of inner beauty and kindness.