Polymarket isn't exactly the best metric of prediction. These people are all degenerate gamblers trying to make some money off the next election. There's a bunch of betting contracts saying the exact opposite as well. Basically, people are betting a lot on long shots hoping to "hit it big" because they're gambling addicts. And don't fool yourself, the type of people using polymarket are OVERWHELMINGLY gambling addicts. Not exactly the type of population subset that accurately represents the overall US population considering the majority of people don't gamble at all, and have no desire to bet money on things like elections.