Here's why:
* Action Replay codes modify game data. They typically target specific memory locations related to gameplay elements. There's no known memory location directly controlling whether a Pokemon follows you or not.
* Following Pokemon is a core feature of SoulSilver. It's ingrained in the game's mechanics and likely wouldn't be easily modified with an Action Replay code.
Alternative Solutions:
1. Use the "Call" command: This allows you to temporarily call your Pokemon back to its Pokeball, preventing it from following.
2. Use a Pokemon that doesn't follow: Some Pokemon, like Snorlax, don't follow you outside of battle.
3. Try a different game: While not ideal, some Pokemon games (like FireRed and LeafGreen) don't have the following mechanic.
Keep in mind that using Action Replay codes can potentially harm your game save file. It's always recommended to back up your save before experimenting with codes.