That is precisely the thing. The link between service and tip was the "fundamental conceit of tipping culture". But no longer. You simply tip for certain kin

That is precisely the thing. The link between service and tip was the "fundamental conceit of tipping culture". But no longer. You simply tip for certain kinds of jobs (e.g., coffeeshop baristas) and not others (McDonald's cashiers). It is pointless to try to make sense out of it; it makes no sense.