Please define "extremely rare". They're found in many products including dental floss, clothing, furniture, carpets, pizza boxes, fishing line, and only-God-knows-what-else.

It's certainly small as a mass fraction of household waste, let's say 0.01%. According to the article, European waste-to-energy plants burn 96 million tons of trash annually. So that's 9600 tons annually of fluorocarbon pollution, which will build up cumulatively in the environment because it effectively never breaks down.