Most of the cost of a book is not the physical pulp or ink that went into making the book, it is in the editing, typesetting, and marketing that went into making the book ready for sale, so ebooks generally should not be much cheaper than physical books.
Having read several self‐published Kindle Direct books that are incredibly deficient in the editing and typesetting departments (compared to earlier traditionally‐published works from the same authors), I find the fact rather obvious.
