Many of them are anorexic. They smoke to decrease their appetite. I can tell you stories of taking care of performing artists - young women. In a troupe of 30 to 40 dancers, ninety percent smoke. Regardless of their age, they go outside to smoke on their break.
Dancers require so much oxygen.
That is the European argument, but that's not really the case. Athletic activity more quickly distributes the toxins in the smoke because athletes breathe more deeply. When they are performing they are not thinking about the fact that they have not had a cigarette lately. To some extent, an increase in their ability to perform is very positive feedback. If the young athlete wants to be ostracized, then smoking is the way to go.