I immagine some kind of tragedy, or fleeing tragedies. Usually it's wars and change of regimes that force some families out of their homes.

Death in the family. Legal issues. Or as Daria said tragedies in general. I've watched a lot of videos about abandoned places, and some houses just seem to be forgotten after the owner passes. Maybe a rift in the family, or the person who inherits the property lives too far away and can't afford to come back. So the property just sits. Vacant. I did see one abandoned house- so full of stuff- that had only been vacant a few years because the parents were arrested. House was put on the market but was disgusting- they'd been arrested for animal cruelty, so many sick animals in the house- so there were no takers. Yeah the animals were gone- but I'm guessing the smell wasn't.