The Tiny MBA is a popular book that was published recently by Alex Hillman of StackingtheBricks.com. He goes through some of the problems publishing through Amazon, where you don’t have direct access to your own customers.
Business Opportunity: While Amazon’s reach is undeniable, this sounds like there could be a business to create a Substack type business for business books. Authors own their own lists of purchasers but still get access to the aggregation of a larger platform.