When you consider that different ebooks and different font selection can result in lines and pages breaking at any random place, ebooks may actually be more expensive to produce.
Nevertheless automatic typesetting and formatting have existed for decades! TeX and LaTeX are ancient and produce better looking results than any book I've ever read on any of my ereaders, and those aren't the only tools in this space.
Whatever people are paying for such "production" seems wasted.
However that PDF is not reflow-able (or changeable in any way) once it's on the device, and that's not what people are buying ebook readers for.