Agreed, but it is (somewhat) justified by the sheer length of the chain (printing house, distributors, bookstores etc.)

FWIW, I wrote and self-published a book on a 99% automated platform (e-book only), and I get 80% royalties.

Another (anec)datapoint: I published a book (this time not written by me) in a more "traditional" way (i.e., on paper). The book is pretty niche, had 0 marketing expenses (we basically only relied on word-of-mouth). We kept the costs low, but not too low (we paid a bit for nice typesetting, illustrations, good paper etc.). We did not even try to put it in bookstores and only sold it via Internet (using an ebay-style platform, not even a custom e-commerce solution; we didn't even had a landing page with a our own domain!). This allowed us to break even after a few months, which I think is insane comparing to the "big book" (aka publishing industry).

His take went from 70% on Amazon to just 7% w/ the traditional publisher.

Of course the traditional publisher handles all marketing and distribution, so hopefully the slimmer percentage of a much bigger pie works out.

But I was amazed at how low the final percentage was.

You can try solving this by industry-wide regulations, but that would make average price of books much higher, and will likely steer readers to other medias, shift revenues to already established writers, or both.