Many, I suspect the overwhelming majority, of the markets are impossible to engage in insider trading in. So it's genuinely just an interesting way to monetize expertise. Chess is a great example. A lot of the money in that market is people turning on the latest chess engines and betting in accordance to position evals, but skilled players can see much more - like how a position that the computer gives as a dead drawn is, in reality, extremely difficult for one side to hold. So the market might give near 50% when it's perhaps more like 65/35. That's quite a large edge. There's also quite a lot of opportunities for arbitrage betting, which is by definition risk free.