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.
It doesn't really matter does it? You don't collect data without consent, period. Why is that so hard to understand? Why don't developers ever push back against this sort of thing? Collectively we build this stuff, we are not 'soldiers following orders' which makes us responsible for what we create. The current actual use is not relevant. Consent and the possible uses are relevant.
Every webserver logs the IP address and the URL visited. Do you think most people know this? Do deverlopers push against this?