The winning prediction market strategy for presidential elections is to buy whichever candidate is cheaper than 50% until a week or two before the election. Candidates adjust positions and messaging to gain ground, so you can reliably buy the dip unless it's a 1980s blowout
The election itself has formed a direct feedback loop with the polls. Politicians tweak policies to force it back to 50/50 because that's the game theoretic equilibrium. 50-50 isn't due to a failure of predictably, it's due to information efficiency in a dynamic system.