Nobody cares about cars killing people and animals.

I think that's overstating it a bit, of course many care, and we have people who are responsible for setting safety standards.
Just because accidents are unavoidable doesn't mean we aren't trying to minimize them and avoid fatalities.

Mandatory safety belts is an example of this. But other than that there are actual scientific studies into road safety, and even city wide implementations of such studies. At least in Europe there is, but I'm guessing USA has it too.

Just because traffic accidents happen, and we obviously need "traffic" to be able to move around, doesn't mean nobody cares.

As an anecdotal example, here (Denmark) the speed limit was increased from 110 to 130 on our equivalent to Autobahn, which may seem like accepting more accidents for convenience or efficiency. But in reality it was to divert more traffic to the safer "Autobahn" to actually reduce the number of accidents on smaller roads.

Traffic safety is as much about psychology as it is about making safer systems.

PPS:
Regarding the animals we have just had warnings about deer, and some places have small tunnels made for frogs.
And there are warning signs where deer tend to cross in almost any country that has them.