Why? It's not Amazon's fault, but rather the decision of the publisher... And I guess it's your loss anyway. I had the same problem (I have to use amazon.de), but hey, better that than nothing!
They wonder why folks pirate. I paid for that book, I would feel well within my rights to find a copy of the book in PDF format (non-DRM encoded) and use that instead. I haven't done that - but there you have it. I paid for a book, I didn't get a refund of about $100 and I can no longer read the book. They stole from me.