Izzet Affinity plays a heavy Island count alongside Underground Sea, so Carpet of Flowers generates a big mana boost off their blue sources to help us keep pace with their artifact engine. Rest in Peace disrupts their Kozilek's Command graveyard-exile mode less but more importantly denies any Goblin Welder-style or graveyard recursion synergy while being generally low-impact but free value against a grindy artifact shell; note it doesn't stop Stock Up or The One Ring which aren't graveyard-dependent. Wrath of the Skies is weak here since their real threats are planeswalkers like Karn, the Great Creator and Ugin, Eye of the Storms that dodge a creature/artifact/enchantment sweeper's most relevant targets less consistently than removal like Leyline Binding. Spell Pierce is often too easily paid around given their heavy artifact mana base, so we trim it for more proactive plans.