Imagine apartments built into what used to be department stores, (Oh, you’re JC Penny 203? I’m at Sears 106). Get those old arcades up and running. Set up meal stations at the food court. Once people actually live there, stores will start to move back in.
If I’m unable to finish my life in my own home, that doesn’t sound like a terrible option.
you have to go all the way down below the dirt to prep a site for residential units. With a toilet, shower, and sink per unit, the density of sewer and water plumbing is much higher than commercial. Fire codes also demand egress points (a.k.a. windows) for every bedroom - hard to do Inside a big box retail space.