Heavy partisan bias. Polymarket predict this quite well. Putting your money on the line is still a thing.
Only if this attracts professional punters. I imagine pros prefer to punt on preductible things like 1000 soccer games they modelled using a million datapoints rather than 1 hard to predict election. A combination of vast predictive data and Kelly Criterion. I imagine the election money was dumb. It may have happen to be right.