Because, if so, then alcohol's ubiquity in society would imply that it is probably responsible (in the sense that substances are responsible) for most such conversions.
Schizos may take alcohol or cigarettes to calm down, a form of self medication. On the long term these may worsen, in the immediate they help. Why do you think they smoke a lot?!? To treat. If you smoke or drink, what do you do after a tough day - smoke or drink, to relax, feels great. Schizos may have a tough day , but not from external stimuli, but from internal stimuli
I would imagine other drugs which produce severe (and stressful) withdrawal could also trigger this. The stress alone cannot be good.