Considering all possible card types in magic at the moment (the normal card types are artifact, battle, creature, enchantment, instant, land, planeswalker, sorcery, and kindred (ex tribal)), we get the maximum hypothetical size of Tarmo equal to 9/10
That's the real reason
Rather, environments act as glorified menus from which you select your next opponent, but this doesnt really hamper the experience because thanks to the random nature of a card game theres more than enough variety in gameplay
We saw a similar issue play out with Peregrin Took, which looked like a great card at first but ended up floundering in Lord of the Rings Limited
Patience is frequently rewarded on in-print product
You can obtain the Mewtwo ex (4-Diamonds rarity) card by opening Deluxe Pack: ex from Deluxe Pack: ex set