Read the article and let a feminist explain it to you:
Epithets linked to women have a habit of becoming sexist insults; we don’t tend to describe men as bossy, ditzy, or nasty. They’re not called mean girls or prima donnas or drama queens, even when they totally are. And so Karen has followed the trajectory of dozens of words before it, becoming a cloak for casual sexism as well as a method of criticizing the perceived faux vulnerability of white women.