Books are not designed to reproduce colors though, and monitors are. If you have aggressive auto-brightness settings, that wouldn't actually make a monitor appear more like a book, it would just make it so the stuff that is actually supposed to look blisteringly white is merely mild. Which, sure, is an improvement for eye strain, but it's more of a workaround than a solution, and since it would muck up color reproduction a lot of users couldn't do this all the time anyways.