Is a buggy powered by wind on the road a car?
Nothing, the more the merrier, its when its forced on people that its a problem. It makes cars less affordable, and sometimes for only a marginal benefit.
Unlike cycle safety there is a case for car safety.
Cycle safety is mostly about protecting the cyclist, something that should not have to be legislated for.
Car safety is important, because when it goes wrong, it can have the results of a weapon. There is more justification for legislating safety here.