For the last several years, OCLC has been redesigning their WorldCat system, especially the free web interface, worldcat.org. Even though I am a librarian, I did not offer them feedback in the process, because, for my library, we primarily use the FirstSearch interface to WorldCat. Had I realized that they were going to discontinue the book review function, I would have participated. They could fault me for not participating; I could fault them for not contacting people who were actively posting reviews to ask us for our input. (It may be the case that there were very few of us. The service was not well-advertised and in fact worked poorly.)
From the beginning of worldcat.org, OCLC has ported in reviews from the company Goodreads. That importing of reviews from Goodreads is continuing. When I contacted OCLC to file my complaint, they recommended that I write my reviews on Goodreads. I have noticed that there is now a link in Goodreads to worldcat.org. OCLC may have cut a deal with Goodreads in order to get the WorldCat link in the Goodreads system, which may facilitate Goodreads users finding the books in their local library rather than being pressured to buy the book. Whether or not that was the price for dropping reviews in WorldCat, the new arrangement may prove to be a benefit to both readers and local libraries.
For me, there are two strong reasons why I posted most of my reviews on WorldCat. First, Goodreads is owned by Amazon. Amazon is already a gigantic corporation which has an outsized influence on the realm of books. WorldCat was an independent, non-commercial space in which individuals could express their opinions and ideas about books. While I occasionally post an Amazon review, I prefer not to supply free intellectual labor to the Bezos empire. I do not consider him a charity to which I should donate my intellectual property.
The second, more important reason is that Goodreads only has books that are available on Amazon. I had written reviews for many items in Worldcat that are not currently in print and are not on Goodreads. I would venture to guess that a majority of the items cataloged in WorldCat are not available on Goodreads. Many of the master's theses and doctoral dissertations that are in Worldcat have no Goodreads records. There are many archival items cataloged in WorldCat that have never been for sale commercially.
For example, many of the texts that discuss the novel A Confederacy of Dunces are graduate school theses which are not in Goodreads. Carolyn Gardner's Comedy of Redemption (OCLC #:31977194), Helga Beste's What's That Crazy? (OCLC #: 54375485), and Jessica Gatewood's Decoding the Body (OCLC #: 173660454) are three examples. I had reviews on WorldCat for all of them.
Worldcat provides discovery to a billion texts (and other items such as DVDs that are available or licensed through libraries), but it just eliminated the ability of users to communicate with each other about those texts on its own platform. Instead, OCLC is now relying on one of the world's largest and most aggressive corporations to provide reviews for the subset of items in WorldCat which are commercially available. Sad. Fortunately, I saved copies of all my reviews on my own computer, so I have not lost the work I did. It is just no longer public.