I often wonder the same about Keith Richards ;-)
As a guitar teacher, I use the examples of these tragic figures to illustrate to my students that using drugs robs one of creative vigor and will prematurely end what could have been a long and brilliant career. The result is that many of my students learn to enjoy a lifetime of music and the fun of playing an instrument while they go on to college and become engineers, lawyers, architects, or military officers, etc. Like that shipwreck poster on Despair.com says, "It may be that the purpose of your life is to serve as a warning to others." That's certainly the case with Kobain, Hendrix, Morrison, and others.