A few factors you have to take into consideration.
1. Addicted cigarette smokers will often chain smoke cigarettes one after another. Not only are they chain smoking, but they are chain smoking without allowing their bodies proper time to heal. A smoker can easily go through 1 pack of cigarettes a day. But it’s an endless cycle of smoking one cig after another day after day that gets people in trouble. If a person just smoked 1 cigarette a day, there’s a good chance that person will still be in good health depending on what their other lifestyle choices are like.
2. Weed smokers like myself who smokes everyday aren’t smoking joint after joint, or blunt after blunt, at least most of us aren’t. I smoke around 1 -2 grams a day spread out throughout the day. 1 joint can last me two or three session sometimes. Who really wants to smoke an ounce of Kush a day and spend that kind of money? Shyt makes no sense. If you smoking 5-10 blunts a day then yeah, I’d expect your health to go to shyt eventually. Being that level of stoned isn’t even fun. It will be interesting to see how long Snoop lives because he really enjoys blunts. I’ve 86ed blunts all together, I smoke out of rice papers only when I roll. So yeah, most weed smokers are no where near smoking so much weed where health problems become an issue. Mainly because no one wants to smoke THAT much weed.
Lastly Cigarettes have additive chemicals that just make the product much worse for your health. With dispensary quality weed you don’t have to worry about that. Then take into account the addictive properties of cigarettes, and now you have a smoking product that is 100x worse for your health than marijuana ever could be