More joint households have both members in the work force limiting the amount of shopping being done between 9-5. Add to that the ease of ordering shit online. All of which is on top of malls requiring minors to be accompanied by adults. Add it all together and the result is noone goes to malls anymore.
Plus social media and the internet. Malls used to be teen hangout places but now there are a million more options that don't involve the hassle of actually going somewhere.