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Those old homes are usually used as storage for things that don't fit into their new, urban homes. The market value and taxes are low, so there's no point in selling.

Then eventually, without realizing, you have gone there for the last time, and there's nothing left to move to your new home.

Alternatively, the last old person who lived in the house dies or goes into a care home, and their kids (if they have any) never find the time to clear out the old place. There's no one to sell it to, anyway, so they have all the time in the world.