Storage was still pretty expensive, and there we transitions in computing from originally paper terminals to screen and people didn't have a sense of long-term retention of personal messages (I guess many people probably felt that way about SMS messages on mobile). There also wasn't really a way to look at a user's "profile" like you have on Lemmy - to see everything you post in any topic - which a search-engine provided a way to search for your name across a time period.