Wouldn't such an exchange be a good use case for a smart contract? It would make it very transparent, if the exchange is honest. As a history of all bids, payouts and judgments would be recorded on a blockchain. It probably also would do away with the KYC, so everybody could participate. And nobody would have to give away their private data. Thinking about it ... if the smart contract would let users post new bets as…
Such a thing exists (Polymarket) and the whole setup has probably precluded many, many, many people from using it including myself. I got halfway through setup before giving up. By contrast, I signed up for Kalshi and bought 3 contracts in the last 30 minutes. Additionally, smart contracts don't actually solve the primary source of (unaccepted) risk: the oracle.
It only took me a minute to use Polymarket, but I already had the prerequisites above.