It reads to me like he had he simple (relative to today) investment strategies which where profitable, and closed shop when those market inefficiencies started running dry.
He was also, at that point, very old. He started his first fund in 1968. It tells you something about the modern world that you can your fund successfully for three decades, accumulate one of the best all-time records, and you will still have people online call you useless if you bow out in your 70s when your returns go dry for a couple of years.
