In early days, many/most people also read their email on terminals (or printers) with 80-column lines, so breaking lines at 72-ish was considered good email etiquette (to allow for later quoting prefix ">" without exceeding 80 characters).
>>SoftTa+(OP)
One of the technical marvels of the day were mail and usenet clients that could properly render quoted text from infinite, never ending flame wars!