In the examples you gave:
1. "a traffic offense for causing serious injury or death to a vulnerable individual while operating a motor vehicle"
2. "Despite that evidence, prosecutors declined to seek criminal charges against Vanderweit, saying her carelessness didn’t amount to vehicular homicide" - "Careless driving" is a charge they give drivers when the prosecutor wants to make a quick deal and doesn't think they can prosecute anything higher. I wonder if there's more to the story here given that there were at least 13 witnesses who could explain exactly what happened...
3. "pleaded no contest to overtaking and passing a cyclist without keeping a distance of at least 3 feet"
"Current laws in many ways do not give substantial protections to victims struck by vehicles. As legislative liaison for the Maryland State’s Attorneys’ Association, I would welcome any discussion and examine any changes proposed to the legislature. We share concerns about keeping our community members safe on the roads,” said State’s Attorney John McCarthy."
This all assumes, however, that the accident was actually the fault of the driver. In many cases, it's actually not their fault, in which case the lawsuit from the family goes out the window and the sentence also tends to get reduced. The cases you are thinking of probably involved a pedestrian running into the street without seeing the car or a cyclist doing something equally stupid.