The primary reason is the "Drop Rate" issue. In the original North American and European releases, certain cards are mathematically impossible to obtain through dueling. Unlock all 722 cards immediately. Max Star Chips: Buy any card from the password menu.
Sometimes hosts save files for specific practice segments. If you'd like to get started, I can help you find: yu gi oh forbidden memories save file mcr
: Offers multiple "100% complete" saves with all 722 cards unlocked and all duelists available in Free Duel. The primary reason is the "Drop Rate" issue