I also recently googled a quote, found it in a specific page in a book hosted on https://www.pagebypagebooks.com/, and just impulsively clicked through the whole book because it happened to capture my interest, and only "demanded" that I commit to a single page at a time. Hard to explain, but it felt more natural in that every-page-is-a-URL format to trivially bail at any page, without the weird apprehension I get from the same action in an e-reader / physical book.
The website is super old/limited, but if all books were that trivial to access + click through, I think we'd see something more interesting here. Made me wonder how hard it'd be to convert the entirety of Project Gutenberg into that sort of Web 1.0 format automatically.
With books, actioning a recommendation involves
1) getting a copy of the book (digital or physical, both cost money or at minimum the time required to pirate),
2) starting to read it (with the sunken cost of time and/or money + the drive to "give it a chance" both looming over your shoulder, costing you more time),
3) eventually either getting to the end or swallowing your pride and bailing.
I think you'd start to see actually useful systems here if you could even eliminate step 1; make it easy as clicking in from a recommendation directly into reading mode.
Also solves a critical issue for the engine: gauge recommendation quality by how soon people click out of the rec, as opposed to waiting for the user to go through steps 1-3, and care enough to come back and provide a rating. Way more data to work with.
Of course, this all skirts the Actual Problem: the amount of IP law you'd have to trudge through in making enough books this accessible.