For one, land destruction is now red mana's domain, not white's, and current MtG cards are designed to not destroy too many lands too easily because that leads to unfun gameplay
Our secondary combo is Isochron Scepter imprinting Dramatic Reversal plus mana rocks that tap for at least 2 mana for infinite mana and infinite instant casts, which again is infinite damage/draw with Niv-Mizzet, Parun
The decks in Pauper are not well equipped to handle an onslaught of huge monsters in the developing stages of the game
While it must occupy your active slot to get its healing online, I cant think of many Grass decks in the TCG that wouldnt be better without a lumbering shield that not heals itself every turn, but also packs a punch
Most decks dont need more than five or six lands, so holding the extras ensures you always have some discard fodder for your looters