Uh, perhaps successful, smart and happy people who smoke pot don't tend to share that fact with a lot of people, seeing as it is an illegal substance that a significant portion of society still disapproves of? I'd be willing to bet that you have many acquaintances who partake that you have no idea about.
I did say it was anecdotal evidence but I don't know one, single successful person who continued to smoke grass on a daily basis after college and I know a lot of people.