Here's why:
* Battle Destruction: When a monster is destroyed by battle, it means it lost a battle against another monster. The loser of the battle is sent to the Graveyard.
* Graveyard: The Graveyard is the space where all cards go when they are destroyed. It's a temporary location where you can use their effects for future plays.
Important Note:
* XYZ Materials: When an XYZ Monster is destroyed, its XYZ Materials are detached and sent to the Graveyard. These materials are typically monsters that were used to summon the XYZ Monster.
Example:
If your XYZ Monster "Number 39: Utopia" is destroyed by battle, both "Number 39: Utopia" and its attached XYZ Materials (usually Rank 4 monsters) will go to the Graveyard.