Because you can describe the chemical interactions of nicotine with the human body to a high degree of accuracy, while the psychology of human attention in the 21st century is a subject that is very far from that cut and dry.
That's why we invented a pill that helps with the former, but we might never have one that helps with the latter (although that would be nice)
Well this half true at best.
There is the additional addiction of the physical action just like addicts can get addicted to the act of using a needle, but this is in addition to the severely addicting nature of the substance itself.
Any drug that affects dopamine has the potential to be highly addictive. Nicotine is one such drug.
I guess your comment is case in point. People still don't understand psychological addiction. Yes, nicotine is addictive, but it's a small component of cigarette addiction. If it was just about that then patches would be 100% effective (in reality their success rate is dismal) and people who never smoked would use patches to get a "hit".
So I guess you could think of it the other way around. If you can believe scrolling is addictive then you should also be able to believe that putting a stick of burning plant matter in your mouth is addictive. Once you open your mind to the reality of psychological addiction you'll see it everywhere.
Nicotine is not very addictive. Cigarettes is about the physical addiction.