People want them because after their done collecting all the Pokémon on finished the story and stuff the next best thing to do with your game is to hunt for Pokémon that are much much rarer and people trade with a lot. It’s also to really cool and I Ben though it has no actual advantage like the pokerus for example, it’s still a big aspect for trading and it’s just a co thing that people like to collect in Pokémon games
