It hurts society, but when the damage is spread out over tens of thousands of citizens, it can take a lot of effort to distract them from their day of work and taking care of kids to come together and decide to raise enough money to purchase the empty land and turn it into a park or something the community can use like dense living and services people want.
Just because something exists doesn't mean the market is working. Central Park doesn't exist because it was "economically viable", some things are difficult to put in monetary terms and especially when it requires voters to get together to come to a concensus.
The empty mall lot owner can probably keep re-financing the land and using it as a piggy bank since property values are on a tear in the Valley...what do they care how little value it provides to nearby and prospective residents.
