Once upon a time you could smoke everywhere. Hell, high schools had smoking lounges. Everybody smoked. I actually remain a bit puzzled about why people start smoking these days. I'm not being judgmental, I'm just genuinely curious. When being a smoker involves always having to find a moment to duck out of wherever you are to light up outside, it just doesn't seem that fun anymore.
If I were less lazy I'd peruse the internet for supporting evidence, but I'm pretty sure the answer is: people start smoking as teenagers, and teenagers have always had to duck out of wherever they are to light up. So nothing much has changed on that front. And by the time they're old enough that smoking has become a pain in the ass, it's too late. They're already addicted.
Thus the vast amount of cigarette marketing aimed at young people, combined with similarly vast denials from the cigarette industry that they're doing any such thing.
UPDATE: I started to feel guilty about being so lazy and decided I should go ahead and dig up some Actual Facts™. That turned out to be surprisingly hard (i.e., it took more than the 60 seconds I figured it would). However, a pamphlet from the CDC here says, "Nearly 9 out of 10 smokers start smoking by age 18, and 99% start by age 26." I'm not sure what their source is, but I guess the CDC wouldn't lie to us, would it?