I'd say a mall is a place to go when your intention is to shop as an activity not just as a means to an end. It allows you to constantly browse, with nothing requiring you to stop -- the next store is meters away, food is right there...

Yelp and local transport doesn't meet this niche. Or, it only meets it in a handful of big dense cities that have decent shopping districts. Malls replicate that sort of experience for a spread out suburban area.

Is all that sustainable? Apparently not.