There are other reasons for not switching as well. As an overweight smoker... I drink normal soft drinks rather than diet (sweetener) drinks partly because of vague things in the back of my head about them being carcinogens, but largely because I'm not a fan of their taste.
Regarding smoking - well I've cut down lately, I was smoking 20-30 a day and in November/December, with the exception of two trips abroad where I smoked fully, I cut down to about 20 cigarettes over the two months, due to a challenge from a friend's kid - I simply don't want to move to electronic cigarettes. I love smoking, if it wasn't unhealthy I'd do it forever. I don't love smoking an electronic cigarette, I don't even like it. I'd genuinely prefer to spend a day without nicotine than a day with electronic cigarettes, or nicotine gum/patches.