The non fictional books, especially the self helping/improving one, tend to be very diluted. whatever the reason is. This is naturally in conflict with the reader purpose: extracting value in the fastest way possible.
That is probably why apps like Blinkist or 'OneBookADay' have quite some success. This, by no mean, is to say that books are not an amazing format for the vast majority of content they are being used today, and for the past 700 years.