Imagine someone who causes such an accident. If the sentence is too harsh, such as life in prison, that person will be inclined not to face up to his or her responsibilities, to flee the scene of the accident without trying to come to the victim's aid, even if it is just by calling for help as soon as possible.
Imaginez quelqu'un qui cause un tel accident, si la peine est trop sévère, comme l'emprisonnement à vie, il sera peut-être incité à fuir ses responsabilités, à ne pas se rapporter ou tenter d'aider la victime, ne serait-ce qu'en appelant les secours le plus rapidement possible.