Yeah, my PredictIt winnings (also from betting against Trump after Trump lost) are on a 1099-MISC as "Other Income", which I believe is what gambling would be. Still, the point stands that gambling sucks since not only are you likely to lose more often than you win after fees, but taxes eat your winnings too! But then again, it's hardly gambling when you are betting against Q.
Hilariously, on PredictIt you could see the market inefficiency in action as the site has a cap of $850 risked per bet, but after the election you could make essentially the same bet a dozen different ways. Which party will win? Which candidate will win? Will the winning candidate also win the popular vote? What will be the electoral college margin of victory? Will a woman be elected VP in 2020?
Of all those different ways to make the Trump/Biden bet, the most straightforward ones like "which party wins the 2020 election" had the highest Trump prices, while the less prominent markets like "Will the SC Dem Primary winner win the general election?" had lower Trump prices.
Now, why would I and other gamblers not sell my bets from the expensive 88c "SC Dem Primary Winner" market, and move the money into the cheaper 84c "Which party wins" market? Why would the prices not equalize since they are, at this point, bets on the same outcome? Because I'm already at the $850 cap in the "Which party wins" market. I can't put more in. Or, if I wasn't betting on that before the election, I might not even be able to because PredictIt also caps each market at 5,000 total traders.
In other words, the more obvious markets filled up to their limits earlier in the process and had their price influenced more by people who thought Trump would win, and had less price movement after that due to the distribution of traders already locked into the market. The obscure markets were low-volume before the election, but filled up after-the-fact with people like me eager to find "free money" bets, so the price on the Biden side ended up a few cents higher.