Some of the comments are assuming that all those who smoke pot are irresponsible or unable to do a job if they do smoke pot (this includes people who may only smoke at weekends/parties btw)
We don't regulate alcohol use, and it's quite a lot more destructive for some. I don't get the specific puritanism for pot. Edit: Regulate as in drug testing for past use in an employment context, like what the story is talking about.
My main guess for that special treatment is merely that tobacco and alcohol were global when we started taking care about global health issues, so we left them, but banned any newcomer