I would posit that as you roamed the library scanning for books (something I used to do as well), you have an internal "recommendation" engine that draws your attention to particular book covers or book titles.  That internal recommendation engine might also have you "randomly" scanning books in the Mystery section or the History section, but not the SciFi or Gardening section.

I had not considered the difference between searching in Private mode versus my usual profile.   That leads me to the concept of having various filter buttons available when doing a search, which would correlate to different "profiles" of people.   Just like Pandora is based on a breaking down music into hundreds of components and then categorizing songs along those components,  books could be similarly analyzed.   Then, you could create channels based on authors or specific books and you would get recommendations on other books similar to those.  

One should also have an OPPOSITE profile, which the system builds up as things at the opposite end of the spectrum from what you like.   Kind of like a color wheel.  That makes it easier to check out things out of your normal viewpoint.

I do look forward to the VR library, where one can more closely replicate the feeling of wandering the stacks at the library and grabbing a book, perusing a few pages to see if it grabs you, then finding a nook to read it.