Why Incest?

No.10906608 ViewReplyOriginalReport
I thought that there was supposed to be something called the Westermarck Effect that discouraged incest between relatives that grew up together. But while it's almost understandable that it happened anyways in the past, especially among royals, due to misunderstanding how it affected the children born of such unions, why do we still hear tales of siblings or cousins that grew up together having "relations", despite KNOWING the risks? I just don't understand WHY.