Maybe it means books weren't all that important and they should indeed have been blog posts all along, like on substack. For example as Sam Bankman-Fried has said: "I think, if you wrote a book, you f---ed up, and it should have been a six-paragraph blog post."
Though I have read a few non-fiction books that probably could have been condensed into a single chapter. Unfortunately there doesn't seem to be much of a market for mini-books like that.
For that matter, I've also read fantasy novels that were longer than the entire Lord of the Rings and might have been better as a shorter novella.