Or, possibly, just a recognized incalculable risk. The frequency of natural impacts is known and not expected to be subject to rapid change; the frequency of impacts by manmade objects doesn't really have a long history of constant conditions or conditions that are not subject to change over the life of the contract.
It's not uncommon for insurance to cover damages other people are responsible for (and in exchange assume you right to collect from those parties.)
I mean, it's not like there isn't a human liable for theft, and that's a pretty common coverage in both homeowner's and renter’s policies.
Good point. I guess the logic is that a burglar is unlikely to be doing particularly well for themselves in life, and so may not be able to compensate you for your loss.