[unfamiliar]

Some of those "low density" books are actually about changing your emotional responses or embedding an idea though. Sure you can distill the entire book down to a couple of pages and get the core idea, but your lizard brain isn't going to actually absorb the idea and put it into practice in your life. A lot of the repetition in self-help books in particular is about reinforcing the idea in multiple different contexts and building a proper representation of different behaviour in the reader's mind.