The Rosh Yeshiva of one of the biggest yeshivos in America said: “Any girl that says they will not marry a boy that smokes, will never get married”.
Most bochurim that smoke stop not too long after they are married. In our society, it is something that is done in the “bochurishe setting”, and is not a chronic, permanent thing. You can see that it is not too common for an older yungerman to smoke. By the younger crowd, however, it is very common.