I do not have data, but from first glance, if anything, the overall demand for self-help and self-improvement increases Y/Y. We can correlate it with a sharp drop in alcohol sales, or raising revenues of therapy industry or fitness industry. YT and podcasts still looming too.
But the form of books … Yes, by some reason it collapses. I personally attribute it not to “people realise those guys are salesmen”, but with the fact that none of really good ideas were produced by such books for a while. Now anyone who really has a new angle or new idea to say — they go straight to YT/podcasts, bypassing writing a book altogether. Because of this, me personally, when I check bookshelves, do not see any really new or interesting idea published in the field.
Your comment gave me an idea. First, start with this assumption: Self-help is "someone trying to sell an idea that may improve your life (health, business/wealth, relationships)". Second, consider the mediums that we use to sell self-help. Traditionally, it was in-person/live events. Basically, 100 to 1000 people sit in a big room and listen to a person talk on stage. Usually, there is some Q&A, raise your hands for voting, etc. Now think about the revenue side: How do you scale that business? Publish a book with the same ideas. The in-person events create a personal brand, and books help you scale the business.
Next, consider the mediums for selling self-help: (1) in-person events, (2) books, (3) YouTube. (1) scales the least, but has the highest branding building effect. (2) scales medium, because it costs money for the customer to buy the book. (3) scales infinitely, because it is nearly free. Further, the most financially successful YouTubers first build a personal brand, then begin sell product placement by sponsorships. Further, they also begin selling "merch" (channel merchandise). That is the real gold mine of YouTube. Even sponsonships for most channels with less than one million subscribers pales in comparison to selling "merch".
About (1) (2) and (3) above, I would say that humans are usually more influenced by [the most] (1) seeing a person live, [next most] (3) seeing a person on video, and [the least] (2) reading their book. Thus, it seems logical that YouTube will replace books for self-help.
Without reading the article, my first instinct (after writing the above) is that self-help books are not being replaced with AI/LLMs. Instead, they are being replaced by self-help YouTube channels.
I'm curious how correlated they are to decline of books in general