If a bochur arrived for an interview at a kollel/yeshiva, he would be told that if he chose to one day to dress in jeans and a tee shirt, it would be considered unaceptable and he would be sent home and be subject to dismisal. Why not do the same with smoking? The easiest way to stop smoking is to not start.
In addition, how can a bochur sitting and learning afford cigarettes?