I've read plenty of books that I've chosen not to write reviews for. I don't like spending time writing about stories I didn't enjoy, so I have a lot of DNF's and 2 star reads that I haven't reviewed. Occasionally I will read a story simply because it isn't in my review pile and I won't feel obligated to share my thoughts once I'm done, so I don't review those either.
The majority of stories in my read pile that have no reviews are audiobooks. Of the 45 that I've listened to, I've only reviewed 2 or 3. When I write a review, I like to be able to go back and reference certain things I want to talk about or to double check the spelling of a name or city. I can't do that with audiobooks. Also, they don't come from authors or publishers and they typically have older release dates, so I don't feel any pressure to review them on the blog.
Here are some of my favorite reads that I've loved but never written reviews for.