Unfortunately, we also have decades of built environment that strongly assumes most adults can and will drive. We have significant segments of the population for whom their choice of car is tied into their identity and ego. We have an assumption that many jobs can only be driven to, or even require driving on the job.
We don't have even the political willpower to take away licenses from obviously unfit seniors, much less able-bodied working adults.
People get away with a slap on the wrist for vehicular manslaughter because what's the alternative? Ruining a second life by causing the perpetrator to lose their job? When they already feel terrible about what happened and isn't that punishment enough?
I don't really see a way out of this other than what is already happening in a lot of places, which is trying to break overall car dependence so that taking away a license (or making the tests hard enough that way fewer people can get one in the first place) is no longer a death sentence.