Decentralized prediction markets also offer global liquidity, so the counterparty can be located anywhere on earth. Also the friction and fees should be much lower. If someone in Mongolia wants to bet a million dollars against someone in Colombia today, it’s extremely hard to do without a blockchain (think about the fees and time to wire the money, who would you be wiring it to, etc). Prediction markets are not just for gambling, by the way. They could be used for earthquake insurance, for example.