Cost of production
This seems to assume that the market for a eBook is only limited by price. For a mass-market novel, that may be so, but it's not always like that.
I once worked for an academic publisher and their marketing strategy was to get colleges running courses to make one of that publisher's books the set text, and wrap their course around the book. As well as selling books to students, the publisher provided support material to the colleges such as online tutorials. In effect, they marketed an information package to colleges, often for free. Making money by selling books to students was just the useful side-effect that paid for all that marketing effort.
Once a publisher has persuaded a course leader to adopt a book as the set text, they can charge a high price for it, limited only by what the market can stand. Some students won't buy the book at all, and will attempt to share someone else's copy, some will buy it second-hand, maybe not the current edition, but some will buy it new. The number of new books sold will be some value less than the total number of students studying the courses that have adopted the book. As the publisher, if you reduce the price, a few more of those students might be willing to buy a new copy, but that's about the only control you have.
Biting the hand that feeds IT
