They should just drop the bracketing entirely and give 70% to the authors in all cases, instead of the continued predatory gouging you’re suggesting.
Larger authors are not compelled to agree to these terms sure, but if you’re a smaller publisher or author trying to get your work out there and noticed, it can be hard to gain ground without selling via Amazon.
OTOH, I published this book after about 7 years of weekly blogging, mostly about Emacs, so I think that everyone who might be interested in my book could easily know about it. And an intermediate Elisp textbook is rather a niche thing.
It's not as if Amazon is unaware, they'll fix their pricing system if enough people reject it.