I think the evidence from the financial markets is a bit weaker.
First, let’s imagine predicting that the forecasting platform will stop operating and assume that forecasting is only incentivized by points on this platform. The reasonable prediction is that platform will continue to operate because otherwise, points will become meaningless. Same about predicting existential risk (because if it occurs, one won’t be able to claim a prize).
The US collapse will be devastating for the financial markets (plausible to me unless the USA will gradually lose power and importance, in which case interventions are less crucial). The incentives assumption seems plausible to me as well. So the market might not be a reliable predictor of it.
I am pretty confident that’s wrong. The disanalogy is that with financial markets, you can presently withdraw money and move it to safer assets or spend it on present consumption.