https://www.techdirt.com/articles/20200902/14401045237/content-moderation-case-study-amazon-alters-publishing-rules-to-deter-kindle-unlimited-scammers-april-2016.shtml

Summary: In July 2014, Amazon announced its "Netflix, but for ebooks" service, Kindle Unlimited. Kindle Unlimited allowed readers access to hundreds of thousands of ebooks for a flat rate of $9.99/month.

Amazon paid authors from a subscriber fee pool. Authors were paid per page read by readers -- a system that was meant to reward more popular writers with a larger share of the Kindle Unlimited payment pool.