Prediction markets work just fine already, thanks. The blockchain equivalents are a terrible use of the technology, since they need to use external sources to get the results of markets. This means either trusting a centralized service (and so negating all of the advantages of a blockchain) or some complicated web of voting for the results (open to manipulation and over-the-top complexity)

Meanwhile, existing systems like Betfair's betting exchange have been working for over a decade.