Yes. That was the weird claim. I find hundreds of books about each thing I want to know about, and don't have the time in my life to read even a tiny fraction of them. What are these interests that fall entirely outside of the range of things that people have written about?
To be clear and honest: I don't think it's really true in the way it's meant.
I think people have gotten in this mode where they're only interested in the things that are being pushed in front of them by a feed, whether that's advertising or social media. It isn't that they lack books about things they are interested in, it's that they lack interests unless they think that following that interest could result in social capital. Seeing somebody getting those updoots on the feed creates the interest.