"Why do people drive drunk?"
This is an absolutely awful situation. I do believe the technology exists to determine whether or not you are too intoxicated to drive. Some people are required to use it to be allowed to drive.
I wish I knew more about the situation like whether or not the driver was a repeat offender. Now this kid's family will have to bear the sadness of a young life lost and will always wonder what might have been if this stupid f'n communist a-hole dirtbag c**k s****r hadn't decided... his selfish f'n need to be somewhere was more important than the safety and well being of his fellow man.
That's why they drive drunk.