First of all, many people need a while to drop them completely; there is a learning curve to vaping, one might not get enough nic in the beginning, or not enough supplies yet, etc.
The other thing is, there is more in cigarattes than nic, and about 20% of all vapers find they can't go without some form of tobacco. However, about every other form of tobacco is better than smoking cigarettes. And since vaping takes care of the most pressing need, that is nicotine, smokeless tobacco does the trick for many of those. Have a look at the smokeless section of the forum.
The other thing is, there is more in cigarattes than nic, and about 20% of all vapers find they can't go without some form of tobacco. However, about every other form of tobacco is better than smoking cigarettes. And since vaping takes care of the most pressing need, that is nicotine, smokeless tobacco does the trick for many of those. Have a look at the smokeless section of the forum.