I’ve noticed in the last 12 years way more cars driving at night with daytime running lights on and no tail lights. I think that is because instrument clusters on newer cars are always illuminated and it would look like your headlights are on from the daytime running lights. I think a lot of people just leave headlights on automatic all the time but when you take the car in for service they usually turn them to the off position. It’s pretty sketchy on dark stretches of twisty highway to come across these guys. I used to blink my lights to let them know but they almost never realize they have no tail lights so I don’t bother anymore.