I feel like this is missing any mention of the history of KV stores. Unix came with an embedded database (dbm) from the early days (1979) [0] which was rewritten at Berkeley into the more popular bdb in the 80s. [1] Sendmail was one of the more common programs that used it. And then when djb built his replacement for sendmail, qmail, he invented cdb. [2]
[0] https://en.wikipedia.org/wiki/DBM_(computing)