It's incredibly prevalent but I'll say it's perhaps genre-based not author-based like you are suggesting where it's just authors I've selected. Most of what I read is romance (a wide variety of it) but there's some young adult thrown in there and those two markets are ripe for exactly what I'm talking about. I read hundreds of books in a year by countless authors.
Sometimes what they will do too is have too many books in a series that they consider interconnected so you want the answers to something big from book 2 you need to get book 7 to get that and most though not always the quality of the books suffers the more the author drags it out. Honestly that's normally not a huge deal because a lot of people like more books but you don't want to feel stringed along where you just have to keep purchasing to get things and there are books where that happens. Most complaints I see are when the ebook is under 150 pages or less but 60 pages is also a common length (it should really be called a novella but the point becomes the same).
I'm not saying I blame the authors but that there are both sides.
I once read a book through Kindle Unlimited where the heroine was raped by the hero's brother in very graphic detail 49% in. I DNF (Did Not Finish) right then and there and returned to Kindle Unlimited which I hardly ever do that because I like to finish my books. You bet your butt if I had just purchased it I would have done the same. That was not listed in the trigger warning (which is common among e-books with sensitive topics) no mention of "dark".
Not quite the same as what I had been talking about the length of this book was perfectly fine at 346 pages. I got it through KU but the list price is $4.99. Here's what my review had (and blessedly eReaders make it easy to search this stuff because I sure didn't actually count it lol):
Murmur(s)=111 times according to my Kindle
Mutter(s)=87 times
Grumble(s)=28 times
Whispers=45 times
This is also from a best selling, USA today, Wall Street Journal author (according to her Goodreads page). Oooh I was so tempted to return it just for the above stuff but I pushed through it because I wanted to know how it ended. If it wasn't in KU I may have returned it IDK, it was a very frustrating read. I think if this had just been solely a published physical book the company might have picked up more easily on just how prevalent the authors lack of variety was. Seriously the author in that book never once said "He said" it was "he murmured"...but it became comical after a while.
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If I had to maybe describe the situation it's more like ebooks have become a victim of their own success. They allow for many authors to be self-published and get their stories out there, they allow for people to perhaps read more than they ever could realistically but they also can allow for actions (both on the author and on the reader) to come out. It's sorta become a really bad cycle I would say because I don't think then intent from many avid readers is to leave the author high and dry (and
Amazon pays attention to how many returns you do) nor do I think many authors are trying to leave their readers high and dry but it can certainly feel that way on both.
As for someone mentioning "just get it from the library" even though they were originally talking about a physical book I do that a lot but not all books are found within libraries. I have several library systems at my disposal in my area and one of the interconnected very large series I was reading by an author I had to buy (when the book was $0), read through Kindle Unlimited for other books (and eventually the author left KU so it was good I got those when I did) and borrow from 2 different library systems for their ebooks because the whole set was not available in one spot.