The college smokers that do smoke cigarettes do so because they want to fit in with the crowd of smokers because they think it's cool and the hip thing to do.
Some of those smokers plan to quit smoking after they graduate college although once people do get started smoking it's hard for them to quit.
I've never smoked while in college so it's not every college student that smokes but some do.
The do it because other college students are doing it.