Because you can use statistics to analyze random events. A claim that your system requires resources on the order of $100,000,000 to breach can be converted, as

Because you can use statistics to analyze random events. A claim that your system requires resources on the order of $100,000,000 to breach can be converted, assuming a rate of $300,000/engineer-year to a statement like: "Your system will require on average 300 engineer-years to breach." If the first person who tries is able to breach your system after 1 engineer-year that is an indication that maybe your calculations are incorrect. If it happens again after 1 engineer-year then you have almost absolutely incorrectly determined your true failure rate. If it repeatedly happens over and over again then you are wrong and, conveniently, you will promptly go out of business as people arbitrage your lies. If, however, your analysis is correct, then the probability of getting unlucky multiple times relative to your true failure rate is highly unlikely and the outcomes will stabilize in the long run. Assuming you did not set the payout so high as to be instant death, which I did suggest in FireEye's case as FireEye can, in fact, support a $100,000,000 payout, it provides a relatively sound, objective, statistical basis for inferring the actual cost.