Comment by hatthew

Reddit alone contains about the same quantity of text (~10 billion posts * 10 words per post, vs 1 million books * 100k words per book). Messaging and document platforms (google docs, slack, discord, telegram, etc.) probably each have 1-3 orders of magnitude more than reddit. To your/GP's point though, those private platforms probably haven't been slurped up by LLMs yet.