Prediction markets very often have house odds, even if the market runner is not the house. When you bet on events, the people who can influence those events and are also betting alongside you are the house. They know or can even decide later what the outcome will be, and yet you are betting against them.

This is often called "insider trading" instead of "house odds", but it is ultimately the same thing, the same moral hazard. And note that this is illegal, both in the stock market and in commodities trading - though enforcement varies, and is not very easy anyway.

I'd also note that there are significant problems with random reward games / gambling even when there is no house advantage. Gambling addiction is a real problem that destroys some people's lives, just like alcoholism. And people can become addicted and lose their houses by playing poker just as much as they can by betting on roulette.