Maybe 10 or so years ago, was a real push to convert old malls into apartments or low income housing. Turns out it's not that easy. Those buildings were built with minimal plumbing, just a few public restrooms and limited water service for the food court. There's just not enough water/sewer to supply more than a small handful of apartments. You'd have to tear up significant portions of the building to run all new plumbing for all the kitchens & bathrooms. And that assumes the underlying city infrastructure that runs to the mall could even support the new water & sewage demands in the first place.

I'll grant you, it is a cool idea. It's just not nearly as simple as it sounds.