Here's why:
* Mystery Gift events have specific time limits. These events are usually tied to specific dates or periods. Once the event ends, the ability to receive the mystery gift is gone.
* The servers that handled Mystery Gifts have been shut down. The servers for the original DS games (including HeartGold and SoulSilver) have been discontinued. This means there's no way to connect to them and receive mystery gifts.
However, there are still some ways to obtain certain Pokémon or items in HeartGold:
* Trading with other players. You can still trade Pokémon with other players using the Wireless Adapter or DS Download Play.
* Using the Pokéwalker. The Pokéwalker allows you to catch Pokémon and collect items that can be transferred back to your main game.
* Using cheat codes (if you're playing an emulated copy). Using cheat codes, you can potentially obtain items or Pokémon that would have been available through Mystery Gifts. However, this method is considered cheating and may affect your enjoyment of the game.
It's important to note that the availability of these alternatives depends on your specific situation and playing environment.