Sometimes, to get where you're going, it's helpful to see where you've been. Keeping the history of this thing we call "Agile" is part of that.
Also, periodic discussions arise where someone says "I was agile <mumbly> decades before the Snowbird Conference." Well, yes and no. Upper-case "Agile" was coined, as far as I know, at Snowbird. But it wasn't invented out of thin air. It was built on things that people had found to work, going back decades, in not further. Keeping track of these things is also valuable.
Iterative and Incremental Development: A Brief History by Craig Larman and Victor R. Basali (http://ftp.rta.nato.int/public/PubFullText/RTO/TR/RTO-TR-IST-026/$$TR-IST-026-ALL.pdf)
- NATO report on Evolutionary Software Development