I agree. Airbnb is not a hotel chain / franchise, last minute fully refunded cancelations make cost-of-doing-business guesswork and extenuating circumstances are so broad that it's beginning to seem as if anything goes in spite of the host's cancellation policy. There is a reason hotels are so much more expensive they do not absorb the risk, they factor it into the price, unlike the cheaper listings on Airbnb. And Airbnb is always suggesting hosts make their listings even cheaper than they are.
As for guests it's so irresponsible to expect the host to take the hit for them. I have never traveled without insurance, domestically or internationally. It's less than .cents on the dollar, a cup of coffee costs more.
Airbb should definitely team up with an insurance company and offer it as an add-on. Makes it easy for the guest, just a click away! And I suggest Airbnb highlight the importance of this with a note saying: "It is highly recommended that you purchase trip insurance in case you need to cancel your trip. Please read the host's cancellation policy.
Here's a suggestion for Airbnb - I'm sure a plan could be hatched with this company or similar: https://www.insuremytrip.com/insuring-your-trip/