Does the fact that it's a felony make these maybe somewhat normal people that normally would do the right thing panic and now they know that coming forward could mean a big sentence where as if there was no penalty they could come forward without fear of being locked away for what was in all likely hood a terrible collision...? (accidents can be prevented) I think the case for lessening the charge for this offense could help more than hurt.
But I could also be wrong, guess it depends on what SOCIETY thinks.