Piece part page pay makes sense
If you actually read any ebooks, you know that a lot of the indies are ... not that good.
I read science fiction, but don't like most "young adult" SF, or books riddled with typos and bad grammar. You don't always know what a book is like till you get part way into the book-- why should inferior authors be paid for an entire book when the reader only reads a small number of pages before giving up?
I can also see the gaming of the former system. Have a great intro and super first chapter (hook the bucks) then pad with a lot of drivel since you don't care once you got your piece of the nut. This is a whole lot easier than actually sweating out an ENTIRE quality novel.