There are bits and pieces in various threads on Twitter, but I haven't been able to put the whole puzzle together.
Part of it has to do with "stuffing" Kindle Unlimited books so the authors get more page reads than the book deserves. I've detailed a few examples I found before I even know "stuffing" was a thing. The author publishes a novel or novella or even a short story, but pads the document with other material, which may be previously published stories or even junk filler like recipes and scrapings from the internet. A link at the beginning of the book similar to "Click here for bonus material and special offers!" takes the reader to the end of the book and grants the author full Kindle Edition Normalized Pages ("KENP") credit for pages read. If a 200-page novel is expanded to 500 pages -- or more -- the author gets an enhanced payout. KU is currently paying just about $0.005 (half a cent) per KENP, so stuffing can mean the difference between a $1.00 profit and $2.50 per book. If the book is crap and would not ordinarily even have been read, that profit to the author goes up from maybe $.10 (for 20 pages read).
Apparently there's a crackdown on "stuffing." Apparently Amazon has changed review policies, at least on products other than books. I can't confirm that, though, because I pay so little attention to Amazon reviews. I don't look at mine and can't post reviews, so the whole issue is moot as far as I'm concerned.
I have five novels published with Kindle Direct Publishing, and all are enrolled in Kindle Unlimited. I know this hurts readers who would like to avoid the behemoth, but I have to be realistic. When my books were listed with Smashwords, the sales were infinitessimal. Through Amazon sales and Kindle Unlimited reads, I've made way more than I could ever have made through other outlets. That income is what enables me to keep writing.
My books aren't padded. I don't have any stupid trademarks pending. I write under my own name -- Linda Hilton -- and that's the name I use to post online. The authors who game the system, whether it's through fake reviews, stuffing their books, or other shenanigans, are not my colleagues; they are my adversaries.
They are not friends of readers, either. Who would cheat their "friends" by making them pay, even with their time if not their money, for crap? The ill-gotten KU payments that go to book stuffers are funds taken literally out of the earnings of legitimate authors, those who are writing the books readers actually want to read.
I don't know what exactly Amazon is doing about this, but apparently they're doing . . . something. Whatever it is, I hope it works.