Terrageddon threatens to blow up all lands with Armageddon while Terravore grows enormous off lands already in graveyards, so denying them graveyard fuel is valuable. The extra Tormod's Crypt can shrink a menacing Terravore and also protects your own game plan from Armageddon fallout by not overinvesting in cards you can't rebuy. Arcane Denial is cut because this deck doesn't mind giving you a card in exchange for resolving a threat, and you'd rather not hand them extra draws before a potential land-destruction turn. Your combo often out-races their grindier land-denial plan if you can protect your ritual mana.