Because when we examined the green/blue conflict, nature versus artifice, it became obvious that part of green's identity is its hatred of things unnatural
It also lets you change your next draw, which is a great bonus to both black and blue decks
Certainly threat density is a relevant aspect of a deck but it just doesn't feel as if it is significant as speed or synergy
With the recent rise of ruby/amethyst control, steel has been shaving copies of Fire the Cannons and Grab Your Sword in favor of cards like Beasts Mirror to try and keep up with the opponents card draw
Without it, you would have a fair amount of trouble reliably getting in for combat damage to activate her trigger
Meanwhile, Witherbloom Apprentice serves as a slightly watered-down version of the same effect, but youll be able to play this card early in games as a two drop