I assume that was an oversight
This set is famous for introducing many incredibly powerful Trap Cards, including Yugis Mirror Force and the first wave of Counter Trap Cards: Horn of Heaven, Magic Jammer, Seven Tools of the Bandit, and, you cant forget Solemn Judgment
With R&D always in need of new design space to keep things fresh, theres no reason to keep sitting on an idea as useful as watermarks, or cool as a token-based Planeswalker
That synergizes well with its other abilities, but it also offers great protection if youre an artifact-based deck
If the defender has a land of the relevant type in play, such as swamp for swampwalk, the attacking creature cannot be blocked, even by creatures with the same landwalk ability