And another thing; afaik none of those are second homes or anything like that, they're all literally vacant, owned by banks and such, which leads to another interesting little tidbit.
A couple of states in the US (I forget which ones now, but they're what California types call "flyover states" of course), have started outright giving some of these vacant homes to homeless people, as a first step to helping them get back on their feet.
In doing so, these states discovered it overall cost them less in taxpayer money to give those homes to people than the cost of funding emergency services (food and temporary shelter, for example, among other services) for each person given a home.