As a former Kindle developer, I can say that most of what's mentioned in this article are metrics used to understand how the features are used (bookmarks, highlights, dictionnary, etc.), how much they are used, and in which country. This allows the teams to focus on features that are actively used, and sometimes lead to discontinuing features that see little to no use. Hope that helps.
That's how every company rationalizes the mass collection of user data. "Oh lets collect many terabytes of every user-action in case we need to one day discontinue a feature". It's a book. You don't need to collect and track every fucking action I do to find out if your stupid highlighter is being used in Poland.
Privacy LARPers are a tiny segment of the market, the average person doesn’t really care if their ‘usage of the highlighter function is tracked’