Lost Art Press specializes in fairly niche woodworking content. All authors get the same 50/50 profit split deal. Their books are printed with great care and quality, and the content is some of the best woodworking content available.
(I liked it so much that I ended up buying physical copies of all 3 books in the Anarcist's series)
Bookstores pay 60% of the cover price to the distributor who typically pays around 50% to the publisher.
Then there’s the cost of actually producing the book. And presumably things like editing, etc. are considered costs and not part of the publisher’s split. In the end, that 50/50 split probably comes out pretty close to 10% for the author.