The Drow are perhaps the most overused bunch of villains ever. Their entire ability set is one that is supposed to neutralize the advantages of player characters so that characters can have mirror matches against NPC parties without doubling their treasure. With magic items that turn off once they are brought out of Drow controlled regions, spell-resistance, and spell-like abilities designed to specifically negate common player-character tactical advantages, they can easily compete with Player Characters with massively more permanent magical equipment. And that means that they can be fought and killed several times without supercharging party treasure.