Hello, I don't smoke, but I think it's a common habit among those who already smoke. If you have the habit, or we could call it a vice, of smoking and you stop smoking for a long time, you will surely think about smoking while playing. This causes a great lack of concentration and, as a consequence, they end up smoking.
As for professional players, with the passage of time, I think that this habit has been abandoned, since it was previously considered a symbol of virility (without the intention of offending anyone, but that's how it was believed).
Nowadays, professional players have come to the conclusion that discipline goes hand in hand with a healthy lifestyle, which includes a good diet and, obviously, not smoking.