couldn't folks from the UK have gone on Amazon and purchased it all along?
Perhaps, but some of us like to support our bricks and mortar bookstores, so we don't lose them, and that requires said book being published over here.
Besides, I once tried to buy a book from US amazon (because it was an American small press comic anthology for charity, and wasn't getting published over here), and it was a whole world of hassle I didn't need.