This is all a battle of the titans for market share. Each titan tries to capture as many consumers as possible. They use their ability to reach lots of people and sell to them as an inducement to producers (authors, publishers) to feed content into the system. The titan with the best marketing will edge out the others and become a monopoly, or maybe a couple of them share the top of the mountain. Then prices go up; consumers lose choice; authors and editors lose choice.
As to the diversity of reading systems. Like languages...In the US we have essentially one language; in Europe, many languages. In the US I can understand--maybe not agree with--most people. When we have dead trees books all printed in English, we have libraries with books that are always available, for generations. When we have many incompatible reading systems, we rent books at a high price until our devices become obsolete (2-4 years at most), or until the monopolist changes formats. What does this do to our ability to maintain a civilisation? A personal library?
See the free download about epub3 with cogent reasons for having a standard:
O'Reilly's clever marketing strategy is to distribute electronic formats without DRM and in several convenient, standard formats.