My hypothesis is that no one wants to correct them, the way they would someone they don’t fear retribution from. Their friends might fear being ostracized for implying they’re stupid. Their suitors might fear pushing them away for the same reason. They just say it wrong for years while everyone nods and smiles.
I’ve made a habit of noting them in meetings and then privately informing them after. Have heard replies like, “Wait, really!? That’s so embarrassing, I’ve been saying that wrong for YEARS.”
Constantly getting a pass cuts both ways. It’s also harder to stand on their own, since they grow so accustomed to people constantly offering help, and free stuff.