Here's why:
* Suicune is a Legendary Pokémon: Legendary Pokémon are incredibly powerful and rare. They are designed to be challenging encounters, not easily defeated.
* Suicune is a Mythical Pokémon: Suicune is specifically classified as a Mythical Pokémon in HeartGold. This means it's even more rare and elusive than a Legendary Pokémon, making it practically impossible to catch, let alone kill.
* Game Mechanics: The game mechanics in HeartGold prevent you from defeating Suicune in a typical battle. It will either flee or use its special ability to escape.
Even if you were able to somehow defeat Suicune, the game wouldn't allow you to capture it. You can only encounter Suicune in a specific way, and it's designed to be a challenging and rewarding experience, not a simple battle.