Because it is not pleasurable at all? When I was a kid, I saw a couple of friends get addicted to smoking, from the first cigarette. I have seen dozens of acquaintances as well because I was interested in the process.
Even myself tested his firsts cigarettes.
It was so painful. The body reacts violently when you try to poison it. Severe coughs that people try to hide, trying to appear strong while they could not help it making impulsive movements. It tastes like sh*ht, it burns your lungs. You stink, your clothing and breath stinks.
It takes a lot of concious and painful work in order to force your body into accepting that.
For me it was pure stupidity to make a deliberate effort to get hooked into an addiction, so I just did not continue.
I couldn't help but see that this way. I read a lot so I knew what was coming next. It is like casinos not inviting mathematicians or physicist to conferences, as because of their training, they can see the probabilities inside out and never fall in the emotional trap.