This is a common issue in prediction markets: they tend to look nonsensical at the extremes, because if you're betting on 'sure outcome', then the main issues a

This is a common issue in prediction markets: they tend to look nonsensical at the extremes, because if you're betting on 'sure outcome', then the main issues are a) counterparty risk, i.e. the risk that the payout is not awarded correctly, and b) opportunity costs, as the margins can be slim enough and the payout date far enough away that you've got better things you could do with your money.