It's more a question of who the h*ll would buy them, and what bank would mortgage them?

At the point where a home is seriously damaged I think you are buying the property not the house. Basically those folks that are selling are saying we are done.
The question then becomes who is legally responsible for the removal of the severely damaged house. The ones who were paid to take care of it by the insurance or the new owners. Kind falls into that category of buyer beware.
And it would not surprise me that someone would buy a severely damaged house without thinking it thru......

"The question then becomes who is legally responsible for the removal of the severely damaged house. "

The owner.

You do not actually purchase a house, but a piece of land and "the improvements."

Buy trash and you have to clean it up.

Yeah, I would think there is no way someone could get an FHA loan to purchase one of those homes. So I would think a buyer would likely have to pay cash and/or plan on demo'ing the house.

I think in "disaster" areas sometimes special programs are offerred to help people rebuild or to entice people to buy what are nearly abandoned properties.

I also wonder if many of these people in the affected area had flood insurance and how that (i.e. an insurance settlement) figures into selling the property. Or maybe the sellers are taking what government aid (money) they can get and then are able to sell for dirt cheap.