Someone died, and that is a sad thing.
However the full information behind the case is not being presented here. It says the girl was hit as she crossed the road with her mother, something it does not say, for example, is whether they crossing at a crossing area.
Careless driving implies his driving was below the expected standard, but not that he was driving in such a way that was implicitly dangerous.
The reason people are, IMO, so wound up about this case is that in fact the guy should not have been driving at all. But it's hard to recognise the fact that these factors did not necessarily impact the accident. He may have been off the road, it could as easily have been someone else.