Not all casino games are played against the house. The best analogy would be a game like poker, where the house takes a small percent of every pot (the rake). Other than that, money changes hands between players. The game has an element of randomness and luck but there is also a large element of skill. Players have a wide range motivations and skill levels, from casual players and thrill-seekers to professional players.
I don’t know how this works but assuredly polymarket takes a cut, right? So if we were betting on a coin toss on polymarket, the payout would be less than 2 for both heads ands tail after accounting for polymarket’s fee. That’s not different from the rake for a poker game in a casino?