Here's why:
* Promotional Cards: World Championship decks often feature unique promotional cards that are not part of the standard card pool. These cards are not legal for use in any official tournament format.
* Format Rules: Standard and Expanded formats have specific rules about which cards are allowed, based on their sets and release dates. Promotional cards from World Championship decks are not included in these lists.
However, you can use the cards for casual play or for collection purposes.
Keep in mind: If you are playing in a tournament, always double-check the tournament's rules and format to ensure that you are using legal cards.