* The game's mechanics: In Pokémon XD: Gale of Darkness, only certain Pokémon can be Shadow Pokémon. These are predetermined and are usually related to the game's story and villains.
* Shadow Pokémon are unique: Shadow Pokémon have special abilities and moves that normal Pokémon don't, making them distinct. Making every Pokémon shadow would ruin this unique aspect.
* The game's balance: Having all Pokémon shadow would drastically imbalance the game, making it much too difficult.
However, you can still obtain a good number of Shadow Pokémon in the game. This is done through:
* Capturing them: Many Shadow Pokémon are found in specific locations or are given to you as part of the story.
* Purification: Some Shadow Pokémon can be purified to become normal Pokémon, allowing you to obtain new and interesting Pokémon for your team.
Remember: The core gameplay of Pokémon XD relies on the unique mechanics and story elements surrounding Shadow Pokémon. While it's fun to imagine a world with all Shadow Pokémon, it's not possible or intended within the game's design.