This is almost certainly because they are built to ramp up to cast their commander early and thus have mana available to cast other expensive spells
Designer Notes: Because Nicol Bolas is expensive to flip over, this deck includes a lot of extra mana effects to help out
But what really kicks it over the top is that middle part of his text box: Whenever an opponent casts a spell, if no mana was spent to cast it, counter that spell. You dont have to worry about an opponent casting a Force of Will while tapped out, or a free Fierce Guardianship or Deadly Rollick
Offering five mono-color decks based on some of Magics most popular themes, these seem like great ways to get new players into the game
After all, they make up the bulk of colorless cards out there
One of the things to keep in mind when doing the draft is that you need both creatures and spells to make things work