Here's why:
* Unfair Advantage: Some promotional cards have unique abilities or stats that could give players an unfair advantage over those without them.
* Rarity and Value: Promotional cards are often rarer and more valuable than standard cards, which could create issues with trading and deck building.
* Consistency and Fairness: Using promotional cards would make it difficult to maintain consistency and fairness in tournaments.
Exceptions:
* Some promotional cards are specifically designated for use in specific events or formats (e.g., Special Sets for Regional Championships). These will have clear instructions on their use.
* Casual play: You are free to use promotional cards in casual games with friends.
In short, if you want to compete in official Pokemon TCG tournaments, you need to stick to the cards found in standard sets.