Its because you don't understand statistics. Two thirds of those who smoke will die younger due to their smoking (not lung cancer mostly, more likely heart attacks and stroke). About half of them will lose 10-20 years of extra life. But that leaves one third who won't have an early death due to smoking.
So, it's not luck, it's stacking your odds or not.
Same with drinking. There's now very good evidence that drinking (all drinking, not just heavy drinking) is associated with cancers and earlier death. The more you drink, the more likely that is, also due to accidents, falls etc.
But some will carry on anyway, not everyone who drinks heavily will have a bad liver, but some will. So, those 40 year olds drop down of liver disease and Aunty Margaret keeps going (although 70 is not old at all by my standards, she hasn't even lived to the average age).
I don't know how anyone can say lifestyle doesn't count. It contributes to about 40% of cancers for starters. That doesn't mean everyone who has cancer has had a bad lifestyle, of course genetics and the luck element is in there, but it means if you have those predispositions, then a bad lifestyle will stack up your chances worse.
Heart disease, strokes, and cancer are known as multi-factorial diseases. That means they are caused by lots of different factors coming together, one of which is lifestyle. Having a strong heart from exercise, strong bones from a good diet and weight-bearing exercise, avoiding bowel cancer by eating green veggies and fibre, of course some people outrun these things, but many don't.
We know this as people who can't follow healthy lifestyles and live in polluted areas and are poorer and more stressed live far less long and in poorer health for more years of their lives. The fact your Aunty Margaret beat the odds doesn't mean you will.