alt Hacker NewsNot true, polymarket and kalshi have a lot of system bets, basically bets where the other side is the market, and further they take a cut from the money gambled.
There are other things as well, like they control which side wins, so they can leverage trade or even swing trade internally with a few bot accounts, not saying that they do but I don't see a ToC that says they can't.
Polymarket can market-make, but so can you (i.e be on the both sides of the order book). You can't do that in a casino for instance.
They don't control which side wins (UMA voters do). You should read up about prediction markets and in general sport gambling. Sport gambling platforms with a "house" usually derive their odds from pvp markets. Polymarket is similar to a classic order book market.