Because "if you attack us, we'll obliterate San Francisco" is much better insurance policy. And SK has been pursuing missiles for NK decapitation strike for pas

Because "if you attack us, we'll obliterate San Francisco" is much better insurance policy. And SK has been pursuing missiles for NK decapitation strike for past few years with US blessing. So it's also message for US to keep SK on leash and that US ultimately is culpable for SK behavior.