Here's why:
* Re-Fusion's Effect: Re-Fusion allows you to Special Summon a Fusion Monster from your Extra Deck by banishing Fusion Materials from your Graveyard.
* Fusion Monsters in the Graveyard: Fusion Monsters cannot be Special Summoned from the Graveyard. They can only be Special Summoned from the Extra Deck.
Therefore, even though Re-Fusion can banish Fusion Materials from the Graveyard, it cannot retrieve a Fusion Monster that is already in the Graveyard.
Important Note: While you cannot summon a Fusion Monster directly from the Graveyard, you could potentially use other cards like Monster Reborn or Call of the Haunted to bring a Fusion Monster back to the field from the Graveyard.