Here's why:
* Difficulty: Legendary Pokémon have a much lower catch rate than regular Pokémon, making them harder to capture even with the best Poké Balls.
* Special Encounters: They often appear in specific locations or during special events, requiring you to follow specific steps to encounter them.
* Unique Capture Mechanics: Some games use unique capture mechanics for legendary Pokémon, like the "catch rate multiplier" in Pokémon Go.
So, while you can't just throw an Ultra Ball at Zekrom and hope for the best, you might be able to capture it in the following ways:
* Pokémon Games: In the main series games, you might need to use a special Poké Ball, like a Master Ball, or strategically weaken Zekrom before attempting to capture it.
* Pokémon GO: In Pokémon GO, catching a Zekrom might involve weakening it through battle and using items like Razz Berries and Golden Razz Berries to increase your catch rate.
Always remember to check the specific mechanics and strategies for capturing legendary Pokémon in the game you are playing.