Car headlights are typically large sources. Tiny sources like bike light LEDs produce much higher energy density on the retina for the same intensity. Also car headlights spread their lumens out over a much wider area than bike headlights.
Even though a bike headlight is pointed down toward the road, it's not necessarily there when you stop. All you have to do is tilt the bike a tiny little bit, like at a stop light, and when the front wheel turns a bit the light is directed full force into the eyes of drivers waiting at the light across the intersection. Same situation when the bike banks around curves or to avoid road hazards.
Then there's the situation of cyclists mounting strong LED lights on their helmets, a very unsafe and foolish thing to do when riding on the road. Everything they look toward gets the full beam in the face. Maybe OK on a trail, but definately NOT on the road.
People take light for granted. Flash yourself at night with your headlight and then tell me how benign it is.