If the contract isn't something that meets the criteria for an efficient market, then yeah, it's not something that can be used to give reasonable probabilities.
But for something like, winner of the democratic presidential primary, or the proce of gold in a month... then it's genuinely a better predictive model than what a statistician would be able to come up with.
It doesn't provide anything beneficial to anyone but its owners.
For statistics purposes, it gives me something incredibly beneficial. Simply by knowing the price of a contract, I can know with decent accuracy how likely something is to happen.
If you're not in the field, you wouldn't necessarily appreciate how valuable that is.