I'm surprised no one brought up revenue sharing.

I was under the impression there was a revenue-allocation problem that Amazon needed to solve (Kindle Unlimited subscriptions?), that depended on reliable reading statistics. E.g. How many people read book A?

Wish I could find the article, but the implication was there were a ton of publishers attempting to game the system. For example, by publishing blank, very long "books" and having them "read" by software automation.