"Children … initially have difficulty formulating believable lies, but proficiency improves with age. Young adults between 18 and 29 do it best. After about the age of 45, we begin to lose this ability."https://www.scientificamerican.com/article/the-art-of-lying/ …
Maybe: Effective lying seems to need an element of self deception. Difficult to do with a larger body of knowledge, especially as more and more of it becomes submerged wisdom. Disconnection from the dominant cultural storytelling meme energy also likely.