In Yu-Gi-Oh, there are several cards with "You cannot use this card in a duel", such as Chimaera, The Master of Beasts:
Since this card cannot be used in a duel, what exactly is the point of it?
There can be a number of different reasons for cards existing. In the point of Chimaera, it was a prize card from the 2007 World Championships.
It's not uncommon for a TCG to have official cards that are unplayable in any format.
Looking at this link, it appears that all of the cards that have that text are either promotional cards (see Set Sail for the Kingdom) or cards given out as prizes for tournaments.