[joe_the_user]

Once a mall can't be used as a mall, it is pretty much useless and generally gets torn down. They can't be used for housing since people don't want to live in windowless giant buildings surrounded by parking lots (and owners don't want to lower the rent until the desperate move it. Even the city doesn't want to house the homeless there). Malls might have a bit of office space already but the store-spaces aren't really suited for that either.

Edit: which is to say that traditional malls are just terrible because mixed use would be much better. City center buildings, even strip mall buildings, get a bunch of uses. But the scale of traditional suburbans just forces a single use on it.