1. You need enough paper to create an object with a noticeable mass that takes time to work all the way through. Too small or short and it doesn't feel worth it. Make it short enough and people could read it in the book store.
2. People are bad at applying a crystalized abstraction in day-to-day life. They are better at learning narratives and fitting the current situation to the closest learned narrative, and then acting out the part of the protagonist. Instead of explaining a statistic or explicit rule of thumb, it would be more effective to give a bunch of examples where someone successfully applies the rule and is rewarded. Those examples can take up many pages.
People felt 5-10 minutes isn't enough time for something as serious as insurance.. but 25-30 is so long it turns people away... And then 5%, maybe even 10% savings isn't enough to go through the effort, but 25% seems unrealistic....
You need a document long enough to seem informative and authoritative without being too extreme in any way... Then you can slap a price on it and call it a book!
Reading a 3 minute summary, once, I will easily forget the knowledge. But reading about the idea with different stories and other auxiliary information help me retain the principles much faster.
Despite constant complaints about the padding in many non-fiction books (not just business) there's clearly a silent majority who feel like "If I'm going to bother, ugh, opening a book then I want it to be as thick as possible".
For that matter, you see a similar dynamic on the fiction side too with novellas and short stories bring far distant in popularity to novels. (Even though those same people have zero issues watching 22 minute TV episodes.)
Reading a book is not just “downloading a knowledge into your brain”.
Reading is more like executing a program and seeing dofferent result in dofferent people. People will reflect in a different way and come out with different takes, emphasize points, lessons, and takeaways
So maybe your idea has a future...
Then there was the delightful Bluffer's Guides series.
I like shorter novels and short stories myself, especially in SF where ideas matter.