Here's why:
* Monster destruction doesn't directly impact Life Points: The primary way to reduce your opponent's Life Points is through battle damage or card effects. When a monster is destroyed, it simply goes to the Graveyard.
* Battle Damage: When your monster attacks an opponent's monster, and your monster has a higher Attack value, the difference in Attack is dealt as damage to your opponent's Life Points.
* Card Effects: Many cards have effects that can directly inflict damage to your opponent's Life Points. These effects are triggered by specific conditions or activations.
To summarize: Monster destruction is a part of the game's flow, but it doesn't directly affect Life Points. You need to utilize battle damage, card effects, or other strategic actions to lower your opponent's Life Points and ultimately win the game.