There is a website called "Writer Beware" that acts as a bullhorn to let authors know which publishing entities are withholding royalties, which ones do not act in good faith. etc. You get the picture. In the last several month there have been two exposes of fairly well-known publishers (in two different genres and that's important to keep in the back of your mind). Both of them are not paying royalties due to their authors, both of them have been stalling for months (sometimes for years) in an effort to not pay royalties, all the while collecting money from sales of their authors' books.
The accounting system of publishing is unbelievable arcane. I STILL don't understand my statements and I've been writing professionally for twenty years. I trust my publisher so I don't query my statements, but I have to admit then if I didn't, I'd probably stay quiet for a good long while. Because I'm desperate to stay in the market and keep my name out there.
You say, why are the authors being so dumb to keep publishing with an publishing house that is stiffing them. We aren't dumb, we are desperate. Should you be so lucky to get a publishing contract, you are so grateful, so happy you don't have to go the self-publishing route, that you are willing to accept the fact--for much longer than you should--that emails aren't being returned, that checks aren't arriving in a timely manner, and that surely these are accounting errors. The point is that unless you are publishing with a reputable publisher, then you have NO IDEA how many books are being sold. None. You have to take on faith that they are reporting your sales properly. Because you are desperate, you might find yourself essentially writing for free. Some people with these publishers have not been paid, ever, and others have been paid in the past, but are not being paid now. In some cases we are talking thousands of dollars.
The semi-reputable publishers or those who had a decent rep in the past, but are now holding on to your royalties or are essentially running a Ponzi scheme, will give you back your rights. No questions asked. Of course this means that they don't have your books to sell anymore, but I would imagine the number of queries they get in a given week means they will have fresh product to market in a very short time. Will all of these new authors generate as much income as the previous set? This is debatable, but with so many authors getting bounced from trad publishing, it's not a stretch to consider that these houses are going to capture a few decent authors who have a history of publishing and sales. And those authors are desperate.
If you Google the average salary of authors you will get ridiculous article after ridiculous article that says something like the average "take" for an author is on the order of $60,000/year. This is total hogwash, as pointed out in the sobering blog post by the author's guild (https://www.authorsguild.org/industry-advocacy/six-takeaways-from-the-authors-guild-2018-authors-income-survey/). For 2018, the average income was something like $6500, which was down from 2017. That sounds more like it. Because that average author figure includes people like J.K. Rowling, who I assure you is not pulling down $65,000/year. Add a few zeros to that number.
So, as my publisher told me when they phoned me with the good news about my first book, "Don't quit your day job." I was really lucky because I have an ethical publisher. Sadly, I also know that I was so desperate to get my novel published (I didn't have an agent), I probably would have signed with Fraud-Publishers-R-Us.
Because I was desperate.