I also wasn't aware of this. To be honest, it was good reading (skimming) this article because I had a wrong picture in my mind for "Kessler Syndrome". I thought it was more like the Hollywood ("Gravity") version than a slow but irreversible filling of certain orbits with more and more debris, which at some point would could/will start destroying sats in these simply by the impossibility of avoiding all debris.
I have to think about this. "My" sat luckily is at L2...