Why is smoking different? Everyone has their Nisyonos. I get that. Why does the smoker get off the hook for failing his?
For one, here’s a fun fact: Smoking isn’t assur! At least not according to the Roshei Yeshiva of many prominent yeshivos. It might be looked down upon, and you might even disagree with those people who don’t say it is assur; but until BMG, the Mir, Brisk, et al consider it assur, you have a very simple reason why the smoker gets let off the hook while others don’t. Until then, they obviously disagree l’halacha with raboseinu ba’alei hacoffee room.