The technology peaceful war of “which system of reading matter is best” brings forth a very simple answer.
Why spend your hard-earned money, for a piece of technology, that has an active life, of an AA battery? You have to recharge it, obtain updates peculiar to your little machine, and then, if necessary, buy the electronic material, or rent, you wish to read, and possibly with a time limit, before it ‘self-destructs’.
For all that money spent, you could purchase either the hard-bound, or paperback trade version of the real book!
Is this a serious question? The answer is, because when I get on a 6 hour cross-country flight, I don't want to bring four books with me in a carry-on bag. I can pull out my iPad and I have my entire library available at the push of a button. And when I get tired of reading, I can surf the web, watch a movie, or play a game.
I say this as someone that prefers physical books to e-readers. But to say why would anyone every buy it? That's silly.