I'm not sure they need to understand bitcoin specifically to build a risk model, wouldn't they just need general data on losses suffered by various internet hosts due to hacking attacks? Doesn't really matter exactly what is stolen as long as they have a corpus of data on the value of everything that is stolen in this manner. Bitcoin wallets probably fit somewhere in the payoff curve for that.

There are a couple of insurance companies who will give you a quote on literally anything. You may not like their quote, but they'll give you one.