Here's why:
* Game Exclusives: Pokémon games often feature exclusive Pokémon that are only found in one version of the game. Darkrai is exclusive to Pokémon Pearl and Platinum.
* Events: In the past, there have been events where players could obtain Darkrai in Diamond, but these events have ended.
How to get Darkrai (in Pearl and Platinum):
1. Complete the main story: You need to finish the main story of Pokémon Pearl or Platinum.
2. Talk to the Galactic Leader: After defeating the Galactic Leader, go to the Pokémon Mansion in Eterna City.
3. Find Darkrai: Inside the Mansion, Darkrai will be waiting for you in a special room.
4. Battle and catch: Darkrai will be a high-level Pokémon, so be prepared for a tough battle. Use your strongest Pokémon and try to weaken it before throwing Poké Balls.
Alternatively, you can try to trade for a Darkrai with someone who has a copy of Pearl or Platinum.
Let me know if you have any other Pokémon-related questions! 😊