It's a luxury building in a luxury area.
I don’t think the problem is just the amount or cost of maintenance but how slow it is: the maintenance staff work on the outside of the building hanging from the top. Safety procedures alone would eat a lot into that work time.
I lived in Isola for a year around 2001 (piazza Minniti), and the direction of travel was already well-understood. Even the centro sociale squatters knew they were fighting a lost cause. I was back a couple of years ago and it's largely unrecognisable, with art galleries and real-estate agencies in place of cheap bakeries and northafrican takeaways. I got lost, and felt so depressed that I've never been back since.
Since this thing is unique, there's no statistics, and the cost can be declared ridiculously high. (Also an additional display of conspicuous consumption.)