Here's why:
* It's a glitch, not a real Pokémon: Missingno is a result of data corruption in the game, not a properly defined Pokémon with its own stats, moves, and abilities.
* No move data: Due to being a glitch, it lacks the necessary code to learn or use any moves.
* Game mechanics: The game's mechanics are designed to prevent glitches like Missingno from functioning properly.
In short, while Missingno might appear in your party, it's not a real Pokémon and cannot be trained or used in battle.