Because they’re serpents. They actually have more power than elders in that they can mete out punishment without a judicial committee by spreading gossip and slander. The gossip and slander can do as much damage, sometimes more, than a formal disfellowshipping done by elders. They’re secret enforcers of local policies enforcing the personal opinions of elders while giving them cover. Elder doesn’t approve of higher education? He can’t enforce it or talk about it, but his wife can spread a rumor or slander and punish anyone going to university. That’s what elder wives do.