The value of one single house is basically negative because of the bad neighborhood, bad surrounding homes, high crime, etc. By buying a larger number of contiguous homes, you can greatly reduce those problems. Sounds like a fantastic idea.
My guess is that this is speculative property investment, likely as part of a private REIT/hedge fund. I bet the buyers plan to turn around and sell these off in small lots (usually 10 - 100 at a time) for a small profit.