Motorcycles maybe, cars have (by now) mandatory daytime running lights, but at least in Germany for older cars it's not mandatory to have lights on during daytime.
Worse, some of the daytime running "lights" are only visible from about 5 m directly in front of the car - plus on most cars, the "daytime lights" setting only switches front lights, leaving the back entirely off. That's a cure worse than the disease.
I remember that one country reverted its decision for mandatory daytime light for cars because it decreased visibility of motorbikes (for which daytime lights were mandatory).
That would be France. The idea is indeed to increase visibility of the most vulnerable vehicles. Motorbike riders behave differently than car drivers, hence it is critically important to be able to distinguish them easily in traffic (we downright suck at evaluating movements of light sources compared to solid objects). This is also a factor as to why always-on daylights are mandatorily placed lower than headlights.
