Here's why:
* Different Generations: FireRed is a Generation III game, while HeartGold is a Generation IV game. The two games are incompatible for direct trading.
* No Wireless Connection: These games rely on physical link cables or the older Wireless Adapter for trading, which are not compatible with modern systems or online services.
To get Pokémon from FireRed to HeartGold, you'll need to use a "transfer chain":
1. FireRed to Emerald: Trade Pokémon from FireRed to Pokémon Emerald (a Generation III game) using a link cable.
2. Emerald to Diamond/Pearl: Trade Pokémon from Emerald to Diamond or Pearl (Generation IV games) using a link cable.
3. Diamond/Pearl to HeartGold: Trade Pokémon from Diamond or Pearl to HeartGold using a link cable.
Important Note: This method requires multiple copies of each game and link cables.
Alternatives:
* Pokémon Bank: If you have access to a Nintendo 3DS and the Pokémon Bank service (subscription required), you can transfer Pokémon from older games to newer ones.
* Poké Transporter: You can also use Poké Transporter (available on the 3DS eShop) to transfer Pokémon from Generation IV games to Pokémon Black/White or Black 2/White 2.
Remember that these transfer methods have limitations and may require specific items or steps. It's best to consult online guides for detailed instructions.