Here's why:
* Ghostly Encounters: The tower is haunted by the ghosts of Pokémon that have passed away. It's a place of sadness and grief, and it's not safe for Trainers to enter.
* Plot Significance: The tower plays a significant role in the story, but it's not meant to be explored. Its closed state serves to build suspense and mystery.
If you want to experience the tower in other games, you can visit it in Pokémon LeafGreen, where it's accessible, and the story behind it is revealed.