I would have assumed its from the rise of gig workers using private cars. Uber/Lyft need to keep cars pretty clean to not be dinged stars, and even package and food delivery can create more mess which may require cleaning (but mostly taxi service I think). I skimmed the article and don’t see mention of that?
True, I believe that’s the reason too, a while ago I used to park in an underground parking with a free washing area, the car next to me used to be clean all the time and the guy washes it every day, one time I asked him about such dedication, he said simply he is an uber driver!