That's a whole other set of problems, I know I've read articles about that too but a 15 second google didn't find it.
If I remember right, the main issue isn't the building shape like with skyscrapers, it has to do with power and plumbing. They're only set up for a certain amount of usage of both, and residential is massively higher so you'd basically need to ripe it all out and do it from scratch. And considering malls are predomenantly just in the middle of empty land anyway, at that point you might as well just get the next bit over of empty land and do it from the get go with the appropriate infrastructure.
That's a whole other set of problems, I know I've read articles about that too but a 15 second google didn't find it.
If I remember right, the main issue isn't the building shape like with skyscrapers, it has to do with power and plumbing. They're only set up for a certain amount of usage of both, and residential is massively higher so you'd basically need to ripe it all out and do it from scratch. And considering malls are predomenantly just in the middle of empty land anyway, at that point you might as well just get the next bit over of empty land and do it from the get go with the appropriate infrastructure.