I have a friend who found a red envelope with some money in it in a book that he'd checked out of the library. He figured it belonged to whoever had checked the book out earlier, so he went into the branch and mentioned it. They said that they could find out the last person to read the book, but no more than that, because by and large, librarians (at least in that system) deliberately avoided keeping long term records of what people are reading, to safeguard privacy rights.
Can you imagine Netflix or Amazon, Google or Facebook behaving this way? Could be that I'm from an older generation, but there was a time when people considered the idea of an institution having a long and complete list of everything you've read more than creepy, it was terrifying. Add in cell phone tracking devices that show where we are, map apps that show where we go at what time and what routes we take, commence sites that show what we buy and consider buying. You know for a while there it was impossible to remove a film from your recently watched list on Netflix? (the tech advice was to just select a bunch of stuff randomly and bury it deep if you didn't want it sitting there for everyone else to see the next day).
Libraries don't play nearly as much of a role in making sure that people can access information privately as they used to, they've been shoved out of the way, but they were far more principled guardians of it than tech companies (I mean, night and day, they were guardians, tech companies are rapacious violators of this principle).