Why shouldn't they? Publishers aren't printing books. Apple does the distribution (electronically) and the payments. This leaves publishers to add what value? Marketing? Editing?

or suing all other phone manufacturers for some stupid UI element.

Stupid to you but it's the little details that make a good design a great one. Apple had their UX employees designing the buttons, getting the scroll velocity right, giving the right amount of bounce to a page change. Those engineers got compensated for their work, now Apple wants to be compensated for its work.