Earlier quoted context omitted.
It's entirely dependant upon volume. According to [0], the average US non-fiction book will sell under 3,000 copies in its lifetime. For the proceeds from that to pay the author, editor, and marketing... Well, that's not a lot of copies to amortize those salaries across. The numbers are obviously very different for a New York times best seller, where physical goods costs will represent a larger fraction of the cost.…
Coincidentally, it costs between $2000 and $4000 to print and market a book. So, what, say $1 per book pays for that. The rest pays the author. But wait! Authors only get a buck or two royalty per book. So why do they cost so much? Use your imagination.
[1] https://www.antipope.org/charlie/blog-static/2013/03/why-i-d...