This depends on:

• Have you use free book review service such as Booksprout (which is where my troll came from)?
• How many books have you published? This is my sixth book and the first time something like that happened to me.
• Are you offering you books for free? (free books, for some reason, stand a much higher chance of getting lower reviews, possibly because some people only download them because they are free and not because they would have ever be interested in it enough to buy it — those are not your readers, those a freeloaders and often trolls)
• What kind of books to you write? Some books are more prone to trolling not because they’d be bad but because some ‘reviewers’ happen to not be able to accept diverse opinions on some topics and the right of authors to express their thoughts. One of the reviewers of my book even said that she was surprised how well the book’s written given all the bad reviews. So the book might be written well and there might be nothing wrong with it (certainly not to the extend of deserving it 1-star) but this has nothing to do with the ratings — that’s just trolling. Like Trump’s voters are likely to troll you if you write something critical about Trump (which happened to me on Reddit where they all but lynched me because of it and I was forced into leaving the platform since it became unbearable).
• somebody who has personal issue with you might get back at you by trashing your book (ad hominem falacy), etc., etc.

There are several possible reasons for why this might happen. I’m a member of several groups for writers and have seen numerous complaints by writers that they experienced this — especially on Goodreads and some also on Booksprouts where I found my troll who then unleashed a full-blown attack on Goodreads.