It's faster and easier. Most of the time I don't have to say much about the book other than "I liked it" or "it was boring af". Also, when I search for a book on Goodreads, I want to see rating, and I read 3-4 reviews. If some book already has 450 reviews, writing one more seems like a waste of time. I wrote a few short reviews, and all of them are for the books which had a very few reviews.