The vacants could be remaining vacant for a bunch of reasons. They could be owned by a speculator type, who bought the house with no intention to fix it and is just timing the market. They could be in bad enough shape due to structural issues that even at a $200k selling price it’s not worth it to fix and flip.

The houses being 2 story just means they wouldn’t sell for as much. I expect adding a third floor would be very expense and not worth it from a ROI standpoint.

The 150k number I mentioned earlier, is location/size specific. It seemed to be the price point around me when a lot of 3bd, 2 story houses started getting fixed up.