Why would a cigarette have a sweet taste?

The smoothness of a cigarette comes from the exact variety of tobacco used. Some types of tobacco are more bitter than others. That is one reason why they use additives, since bitter tobacco is often less expensive to grow, and it is cheaper to use a high-yield but bitter variety and then treat it with additives or blend it with milder tobacco.

Additives such as menthol may give the perception of a cigarette being easier to smoke. Filters also help take away the bitterness. Plus after smoking becomes habitual, you might learn to ignore some of the bitterness.