These markets resolve No on popular market resolution dates, so the percentage of these markets show the opportunity cost of money for markets resolving on those dates.

There are existing markets for this already, but they were created while Manifold was giving loans for long term markets, which caused interest rates to be much lower. And there is no incentive to correct them by buying Yes unless you think other traders will need to liquidate their positions to free up capital, so they do not reflect the current risk-free interest rate.