Except they do. That is the problem.

See for example:

https://m.murciatoday.com/almost_half_a_million_vacant_new_b...

https://www.investigate-europe.eu/en/posts/the-empty-house-a...

It isn't a particularly Spanish problem either: following article about the American version of it

https://www.cbsnews.com/news/empty-office-buildings-doom-loo...