I don't know what reason they could possibly have, tbh.

I imagine that car drivers see the people on bikes and scooters, and just get mad.

They'll say it is for safety or whatever, and I do think people on bikes and scooters underestimate how scary it feels to be a pedestrian and have a bike pass by closely, but if you keep asking questions, it seems like they just want cars to predominate and are threatened by non-cars.