It would always be nice to know what Amazon is up to, but this seems a subject particularly in need of public disclosure.
I'm not suggesting that Amazon can or should discuss the business of individual authors with anyone else. But Amazon should post warnings about specific things it no longer allows, assuming those things aren't already expressly prohibited.
You'd think even Amazon would see the wisdom of that. I understand why it wants general (and sometimes overly vague) guidelines to allow itself the latitude to respond to new situations, but when it finds a specific thing objectionable, you'd think it would make that objection very clear to everyone to save itself time later.
I also believe that Amazon should tell authors exactly why they've been banned.
I think if Amazon's problem were the repetition of the same images it might have mentioned potential copyright issues, but maybe not. The "mislead or defraud" line makes me wish I could see the product descriptions, which might provide a clue.
The KDP help page on low-content books shows no sign of recent change:
https://kdp.amazon.com/en_US/help/topic/GGE5T76TWKA85DJM. Nor does it indicate that any particular practices might be forbidden.
If I had to guess, I'd say that the flood of content may have become an issue. From the article at
https://lowcontentprofits.com/is-kdp-worth-it-in-2022/Is Amazon KDP saturated? Yes, kdp is kind of saturated now! What I mean by that is the very basic kdp niches like Journals, sketchbooks, notebooks, diaries, etc. have now become extremely saturated.
The interesting thing is that this comes from an article in which the author says that low content on KDP is still worthwhile on balance, a recommendation based on the fact that some niches (found in another one of his articles) are still profitable. Also, the author has published thousands of low-content books on KDP. Thousands. (Cringe!)
Since the article was updated on October 14, I'm guessing the author is unaware of some people being banned. But it may be noteworthy that he himself is now working with less saturated areas, like Chinese writing practice books and birthday reminder books. (I'm not kidding.) So he may not have been hit yet.
At a certain point, books like journals with blank space or lines for writing become redundant. How many of those need to exist? Amazon does have a rule against duplicate content, though it's poorly enforced. When the Mueller report first came out, Amazon ended up with hundreds of different versions of the Mueller report, many of them identical (just the report text) and hence redundant. But it took a long time for that to get cleaned up. Anyway, maybe the number of pretty close to identical products finally worked its way onto Amazon's radar.
So those are my theories: saturated market, redundant content, possible product description issues.