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?
But if I can avoid buying a car because Uber, then number of washes goes down or is at least balanced.
You aren’t commuting daily in an Uber, nor driving kids to school and activities with all their gear and car seats. Those are the activities which might have moved the needle on needing Uber level frequency of car washes (but even then, I assume an Uber is washed every other day or so, or perhaps I just have a cynical view of humanity keeping the inside of taxis clean).