Because there was a problem with how you got your reviews.
Many new self published authors are of course thrilled to get a few great book reviews, but are shocked if or when their reviews are deleted by Amazon.
The reason why Amazon delete reviews is not easy to understand from their guidelines, which you can read here in full.
However there are two main areas that cause the most problems. Paid reviews and reviews from close friends.
Paying for book reviews can cause your reviews to be deleted
Paid reviews are clearly not acceptable to Amazon. They state:
We do not permit reviews or votes on the helpfulness of reviews that are posted in exchange for compensation of any kind.
However, it is well known that paid reviews are available, and are being posted. It only takes a few minutes to find a paid book review service on social media or by doing a Google search. While Amazon know some of these of course, they also look for a sudden influx of reviews that are well in excess or what would normally be expected from the number of books sold.
So if you have only sold five copies of your book over a month, and you suddenly receive ten new glowing reviews in a week, Amazon will treat this as suspicious, and will probably start deleting the reviews.
Very few readers post book reviews, and this is why genuine reviews are so hard to get. On average, you could expect one review for every two to three hundred books sold.
When reviews start coming in well above this average, Amazon will probably take a look, and then may delete the reviews.
Reviews from close friends will be deleted
This is where most authors get into trouble, and is very often the reason why book reviews are deleted.
Firstly, Amazon do not accept reviews from immediate family:
We do not permit reviews of the same ASIN from customers in the same household.
However, the clause that cause the most problems is this one:
… family members or close friends of the person, group, or company selling on Amazon may not write Customer Reviews …
Close friends can be defined by Amazon as someone you are in contact with on social media. Yes, they can check this! So if you have asked your contacts on Facebook or Twitter to give your book a nice review, be prepared for it to be deleted. Another connection can be commenters on your blog. I can’t prove this, but I have heard of one or two authors who believe this to be why they lost reviews.
Amazon checks all reviews
Enough to know that Amazon can and do check your online connections, and can classify these as close friends.
Asking other authors is also a sure way to have a review deleted, as any other author publishing on Amazon is classed as a ‘person selling on Amazon’.
Getting honest and genuine organic book reviews is painfully slow, especially if you don’t sell a lot of copies. But unfortunately, this the reality.
Trying to kick this process along by either asking friends, and especially online friends to post reviews, or paying for reviews, will probably end up in your reviews being deleted, and tears shed.