why should PG want to offer ratings or suggestion.
How does a real-world "customer" of PG who doesn't already know a title and an author and who already knows that that book is at PG, find a book they want to read? Currently PG would be ahead even to offer a "I'm feeling lucky" button that simply throws a book at the "customer" at random. Magiccatalog is an example of that kind of "I'm feeling lucky" kind of browsing where "at random" the customer says "H'm that one might look interesting" and clicks on one button to download to their reader device.
"PG is not selling anything."
PG is "selling" their contribution to the world. The price may be free, but that doesn't mean you get anywhere if you are not willing to "sell it." If PG doesn't "advertise" their efforts then would-be volunteers never realize that there is an opportunity to make a contribution to the effort. Others are quite happy to take PG's "advertisements" off the books and substitute their own advertisements so that the end users don't know where the books are actually coming from. It's not *just* that these "competitors" want to use the space to advertise themselves. It is also more profitable to them if PG's efforts fail.