Because this is how the puzzle works. Most of the key bytes are zero. Only the last 66 had to be guessed. And their solution was made public by doing the paymen

Because this is how the puzzle works. Most of the key bytes are zero. Only the last 66 had to be guessed. And their solution was made public by doing the payment. mrb describes it better: https://news.ycombinator.com/item?id=41547443 https://news.ycombinator.com/item?id=41547443