Hi,
Because they wrongly think that they can do both (driving and texting)..... sure they are wrong, very wrong..... In fact very very wrong. I don't think they want to kill they only think that "it won't happen to them" and that "they can handle it" or "it's under control". VERY WRONG !!!!! and when they realize it was wrong it'f too late and someone can be killed. If they'll pass a low that a person who is texting while driving will pay a huge fine (say 5,000 $) and if he caused an accident [any one, even minor] the fine will raise to 25,000 $ it will stop that bad habbit.
Best regards,