I think, if you want to truly understand this addiction, you should dive deeply into the research of what it does to your brain -- neurotransmitters etc.
Those who were not raised in a household of smokers, were not possibly carried in a womb of a mother who smoked, and who did not begin smoking at an early age while the brain is still developing, cannot possibly imagine the struggle one goes through when they attempt to quit, or do quit.
Can it be done? Of course it can. People do it every day. Do they remain the same person they are when they were smoking? Absolutely not.
Many will turn to addictions of another nature. Whether that be food, alcohol, shopping, gambling, exercise, you name it -- they're going to get that boost of dopamine from somewhere.
"It's hard" ... does not begin to cover it. If, for just a minute, you can imagine what it would feel like to *lose who you are* and turn into some other person -- whom you may or may not like very much -- then you may be able to begin to understand.
Smokers are self-medicating. It has side effects, just like every other drug. And with every drug, each individual must weigh the pros & cons. I can assure you there is an almost daily weighing in the mind of every smoker. And on that day that you see them outside, in that moment, they've decided that the benefit outweighs the risk. Perhaps someday, something will change their minds. But one thing is for sure: no one is going to change their minds FOR them.
It may not make one bit of sense to you -- and if that's the case, count yourself blessed. That means you have not had experience with this particular struggle. And your body is thankful.