I have a close friend who published an engineering text book. He worked a couple of years on it and it was well received in his particular field. The book was pirated within months and is freely available on PDF. It's unfair that his hard work is being used globally for free. So yes, having books shut off sucks but so does piracy.
DRM is a ludicrous solution to preventing ebook piracy. One of the first things I learned as a teenager online was that anything that can be read, seen or heard can also be copied. It's only with interactive things like games and programs that pirates have a real challenge.
Books can be copied for sure, but the cost of copying a digital book is negligible compared to the cost of copying a real book. Zero cost of copying makes it possible to give it away for free (e.g. to drive traffic) and monetize otherwise (most digital piracy is business, not charity).
In the physical world, copied books are not given away for free typically because the cost of copying a book is relatively high.
Copyrighting digital items is a fundamental problem which has no good solution so far.