Pyroclasm's 2 damage to each creature sweeps their swarm of small bodies like Basking Rootwalla, Birds of Paradise, Llanowar Elves, and Wild Mongrel, disrupting their Survival of the Fittest-powered board development. Cutting Werebear removes a creature that dies to your own Pyroclasm and isn't a priority blocker against their aggression. Earthquake is already in the mainboard at 1 copy and sufficient, so redundant copies aren't needed; the extra slot is better used on sweeper density. Armageddon is still a premium card since it punishes their Gaea's Cradle-heavy, land-hungry development plan.