Because these houses are located in remote, rural areas. They have been abandoned because people are moving closer to the cities or the owners are old/dying and they can't continue maintaining them. The money you save from the initial purchase will all come out of the expenses to renovate and maintain the house because a lot of them are run-down.

Of course if you're the type who wants to live in the middle of nowhere, and you have the money and skills to renovate, this can be for you.