Here's why:
* Mew was not included in the original Pokemon Red and Blue games, and thus not in their remakes (Fire Red and Leaf Green). It was only introduced later in the Pokemon Gold and Silver games.
* While you might find ways to cheat in Mew into Fire Red, these methods are not official and would involve external programs or glitches.
If you're looking to get Mew, your options are:
* Play Pokemon Gold or Silver (or their remakes, HeartGold and SoulSilver). Mew can be obtained in these games through the "Mew Glitch" (though this is a very complicated method).
* Trade with someone who has a Mew from a later game.
* Use a save editor or other external methods to add Mew to your game. This is not a legitimate way to obtain Mew, and it can cause problems with your game.
It's important to note that trading a starter Pokemon doesn't unlock any special events or Pokemon, including Mew.