@Nanxing0, @Emilia42, @Sarah977 ,
I would guess that there is a pop up message when a guest tries to cancel that reminds them the reservation is non-refundable. The guest then calls into CS, and are told that if the host agrees they can get a refund, minus the service fee. Of course, the guest is going to contact the guest with some type of story either demanding or pleading for a refund.
BTW, suggesting that guests purchase travel insurance may not be the answer, either. I purchase an annual travel policy from Allianz, because we spend a lot of time abroad. The following is on the very top of their home page:
If guests cannot rely upon an insurance policy to reimburse them for canceled or interrupted travel plans, there will more instances of them requesting refunds from hosts.