Because it's not really a pressing problem. Spent nuclear waste can sit in a swimming pool of water for any amount of time without endangering anyone. And water is so good at shielding radiation that you can even swim in such a pool. After few years the waste is moved to outside casks which are also not a danger to anyone. The only real problem is protecting those places from terrorists and such. But then again we have burnt coal ash sitting in huge piles outside under clear sky, and I would argue they pollute a lot more than a spent nuclear fuel cask does.