[1] provides a good answer to this question.

"The outcome becomes more predictable over time.

This is because the payoff depends on the accurate prediction of an outcome of an event. Therefore, people will put in more effort to come to the most accurate conclusion.

As a larger number of people do more market research to come to the most likely conclusion, the predicted outcome will lean more favorable to one side.

If you place a bet on a coin flip, the outcome will always be 50% heads, 50% tails. There are no external market conditions that will influence the outcome. Luck plays a major role, and this is called gambling.

But prediction markets rely on the collective wisdom held by a group of people on the probability of a future event materializing."

[1] https://cointelegraph.com/explained/prediction-markets-expla...