I've had a fair number of my reviews deleted. They are solid reviews presenting aspects for each and every star.
At first I thought: 'This is the author removing everything that's not a five star review. Bloody idiot!"
I sure some are, bloody idiots that is, but there are probably another reason to delete a review.
An honest review pointing out weaknesses, say a 3.5 star review, simply becomes obsolete half a year later if the author acted on the pointers, rewrote earlier chapter and overall kept up the new and improved standards. In that case that once honest review becomes false.