Why does email outlast chat messages or SMS threads?

Because email is a document, while chat is a conversation.

Chat messages are ephemeral. They're difficult to search, often deleted, and designed for immediacy. Email creates an official record that can be archived, forwarded, and audited.

A chat thread is a conversation in the ship's galley — informal and fleeting. An email is an entry in the captain's official log — permanent, structured, and searchable.