And there's always a chance things go wrong, even with inside information. It would be unwise to go all in.
therefore, the polymarket betting odds will reflect the truth - even if that info is a secret that nobody else but the insider knows. And if this is the case, then even an outsider could make use of the odds as a source of info which would ensure that market efficiency (which is about the flow of information) is high.
So what's wrong with insider trading again?
https://gizmodo.com/checking-in-on-polymarket-bets-on-christ...
Will X country invade another before or after day X? A large enough market changes the answer, as the agent can change the decision. And we can see this kind of thing in many interesting questions.