@Fred13 I've fielded a few of these myself over the years, and honestly the process of dealing with them feels more labor-intensive than any other task of hosting.
I do find it quite easy to understand why the host would not choose to "roll over" the reservation into dates far into the future. That would back him into a corner; Airbnb offers no way of converting a booking into a "stored value" credit, so the only way for the guest to reschedule without cancelling would be for the guest to select dates that may not even be open in the calendar yet. And there's the trap: if for any reason the host is unable to keep the commitment to those faraway dates, and the guest refuses to accept a host-initiated amendment to the booking, the host is forced to cancel the booking and not only remit a full refund but also accept cancellation penalties.
The behavior of the guest is the typical thing one encounters from certain types of people, but this does work as a cautionary tale for both people on both sides of the equation.
Guests: be mindful of cancellation policies before you book, buy appropriate insurance if you can't bear to lose your prepayment when circumstances change, and don't overestimate your leverage when successfully renegotiating your agreement might require you to be seen as a desirable customer.
Hosts: Don't try to cut deals with people who display any refusal to accept the terms they agreed to. Even if you think you're making a generous offer, it'll always come back to bite you in the butt.