Here's why:
* Snivy is from Generation V (Black and White): Pokemon FireRed is a Generation III game. Pokemon from later generations weren't introduced until later games.
* No Trading in FireRed: While you can trade Pokemon in FireRed, you can only trade with other Generation III games. This means you can't get a Snivy from a later game.
How to Get Snivy in FireRed (Using Cheats):
The only way to get Snivy in FireRed is by using a cheating device like Gameshark or an emulator with cheat codes. This will allow you to modify the game data to add Snivy to your game. However, using cheats is considered cheating and may not be accepted by online communities or tournaments.
Alternatives:
If you want to play with Snivy, you'll need to play a Generation V or later Pokemon game where Snivy is available.