A numbers conundrum

On Goodreads The Emperor (Book 1) has 4500 four and five star ratings but The Son (Book 2) and The Thief (Book 3) have a combined total of 500 four and five star ratings. Why would someone enjoy the first book in a series and not want to know how the story unfolded. The Son has 230 ratings and The Thief 300. I could understand if you enjoyed The Emperor you might decide to skip the middle but surely you would want to know what happened in the end. Maybe the fact that most of the ratings will have been driven by free issue e-books from a PR company explains it. Prepared to read a freebie but less willing to spend?