There are wiki summaries of most self-help books that have basically the same amount of information. The only issue is a moral one - you're not compensating the author for their advice.
Let's consider that writing a book, in terms of typing, doesn't take that long. However, the perception of value is proportional to the size of the book: are you going to pay for 10-20 pages of information?
Now, let's consider the cost of researching that information. In some cases, it can be the output of years of doctoral research. In others, it's "only" six months of dedicated research. That's six months to research an idea, find evidence, challenge it with alternative explanations, test its efficacy, and determine the best way to present that information. (We won't even talk of the issues of marketing and the other parts of a book that don't involve writing it.)
That is, you need to put together 600 pages of research. You can then distill it into 200 pages or 20 pages. If you distill it into 20 pages, people will think it is less valuable. That is, you spend more time and get less out of it.
(It's something I struggle with. I am part way into research that could increase the productivity of non-great (that is, average or worse) developers 5-25%. The core idea can be explained in 5 pages. The extended idea takes 20. However, it's currently a hypothesis and doing the work to prove it out is estimated at 3-4 months of solid work.
How would I present that information? I can say it wouldn't be a 20 page article or blog post because it's not monetizable. So, how do you change that business model?
Short books for solving a problem that readers have, long books for entertainment.
People will absolutely pay good money (thousands) for a 20 page pdf that solves a painful problem. But they’ll fidget and squirm at the prospect of $20 for 300 pages of edutainment.
