Known risk is an oxymoron. People buy insurance to cover known risk. I would never buy fire insurance, unless I at least considered the possibility my house would burn down. This is the same as before Coronavirus - I knew there was a risk flights, hotels, liveaboards, etc could cancel, otherwise I wouldn't buy insurance.
Your analogy is reasonable on its face, but look at it this way: The insurer sells home insurance policies for X dollars, based on the risk of the average house burning down being Y. If Y suddenly increases by some reasonably certain amount, they can continue selling policies simply by increasing X. But the risk of flights being cancelled due to the novel coronavirus is a moving target--they can't reasonably recalculate the premium they would have to charge to remain profitable, so they just refuse to sell new policies that would otherwise have covered such cancellations. From the insurer's perspective, the risk is not "known"--it can't be calculated with enough precision to enable them to price insurance for it.