This was probably done because Duel Monsters was released before the first OCG set, Vol.1 , though it is not known why so few of the cards in the game have passwords, especially since the game credited at least nine individuals, but only six of them had passwords, and since the game includes 15 secret monsters, but only nine of them can be unlocked with a password
Banlist History Restriction changes recorded for Unicorn Beacon
I'm not sold on these "graveyard hate" creatures that don't actually impact the board- Unlicensed Hearse does it all
Complete Card Gallery All 120 cards from Platinum Rising Rivals, including the nine Pokmon Lv.X, the three Pikachu secret rares and the six-card Rotom subset
And thats only the tip of the iceberg
Owning a Shiny card in the TCG can evoke the same sense of achievement and rarity, reinforcing the connection between the video game and the trading card game