First, many non-book Artifacts have activated abilities, meaning that the addition of the book subtype wouldn't add any unique identifier
It's not exactly going to stop the likes of powerhouse archetypes like Dredge or Reanimator, as those cards enter the graveyard from the deck or hand as opposed to the battlefield
First-edition copies command a significant price tag, ranging between $100 (MP) and $300 (NM), which is a decent price, as copies that are graded as NM often exceed $300
Lastly, Greninja pairs exceptionally well with Gyarados ex as a secondary Ace, bringing additional utility with its Water Shuriken ability
Furthermore, this is the only tempting offer card which uses hidden information, thus giving your opponents opportunities to make mistakes