Whenever dudes start talking about the election prediction markets, I always wonder if they've actually used them before by the way they speak.
PredictIt limits how much you can bet on any given prediction (quite low limits) and has fees. It is why they'll have bizarre results like Hillary Clinton winning rather high.
Polymarket isn't available in the US and uses crypto instead of dollars. So users have to be knowledgeable about crypto and want it.
So these two major election markets, don't clear cleanly, and probably have a lot of selection going on given the market participants.