Here's why:
* Fairness: Using the same set of letters for every contestant ensures that everyone has the same opportunity to win. It eliminates any potential advantage a contestant might have from knowing the letters used in a previous round.
* Challenge: The puzzle is already challenging enough without having to guess which letters might be available. Keeping the letters consistent adds another layer of difficulty and keeps the game exciting.
* Memorability: Having the same letters each time helps viewers and contestants to remember the bonus round and feel a sense of familiarity. It becomes part of the show's iconic format.
* Production Efficiency: Using a fixed set of letters simplifies the production process, making it easier to prepare and manage the bonus round.
While there may be some arguments for using a more diverse set of letters, the current system has proven to be effective and fair, contributing to the overall success of the show.