Because cigarette companies main goal is to get you hooked, while food and drink are basic necessities of life.
McDonald's food was highly addictive (and sugar filled) at one point, I dont know if that's changed or not since then. Everything can be addictive in copious ammounts, alcohol, fast food, soda, junk food, cigarettes, six, drug's. Your body will eventually build a reliance on it, mental or physical.
Whether or not you believe they are healthy is one thing, but soda contains water which you body can utilize, and McDonalds contains fat and calories to keep you from starving. Cigarettes have no beneficial function to your body whatsoever, besides making you feel good.... until you get addicted and the cravings kick in.
Cigarettes have beneficial functions for me. They stop me going ona stress induced rampage throughout new york while I attack some dude played by Tim Roth.