It may be a lack of "social intelligence" as you say, but it could also be a result of Broken Windows Theory (http://en.wikipedia.org/wiki/Broken_windows_theory). What incentive does one person have to organize his/her trash when there are already massive burning piles in the street?
I feel that the concept of the "Tragedy of the Commons" more closely mirrors this aspect of "social intelligence" that the original commenter referred to.
Thats also a major cause. In fact Ugly Indian group has noticed similar effect. When they clean certain areas of the streets and improve it aesthetically, it stops being degraded to its original state more often than not.
