The implication is that the self-help books were scraped from Anna's Archive to train the LLMs, thus the content in the books has been integrated into the LLM and may be regurgitated on command. With the content then being available straight from an LLM, there's no need to buy the books.
" they wouldn't be getting sued and aggressively pursued for takedowns"
I don't think so. That behavior only tells you the modest cost of sending takedown notices/threatening letters is less than the (supposed) lost revenue. Kids I know (I'm a teacher) don't seem at all aware of it when complaining about textbook costs and I kind of vaguely hint they look online for it--nothing like the popularity of napster.
