Here's why:
* Darkrai is a special event Pokemon: It was distributed via an event only accessible with a Nintendo Wi-Fi Connection and a Nintendo Wi-Fi Connection membership.
* The event ended: The Darkrai distribution period has long since passed, meaning you can no longer obtain it through the original event.
There are no legitimate ways to get Darkrai in Pokemon Platinum without a membership card.
Here's what you can do:
* Trade for it: Try searching online forums or trading communities to see if someone is willing to trade a Darkrai for a Pokemon you have.
* Look for a ROM hack: Some ROM hacks for Pokemon Platinum may include Darkrai as an obtainable Pokemon. However, these are unofficial and may not be legal to download or play.
* Play a different Pokemon game: Darkrai is obtainable in other games like Pokemon Black/White, Pokemon Black 2/White 2, and Pokemon Mystery Dungeon: Explorers of Time/Darkness/Sky.
Remember, using cheats, exploits, or unofficial methods to obtain Pokemon may be against the spirit of the game and can be considered unethical.