Honey is not a vegan food because commercial bee farming involves various practices that are harmful to the life and health of the bees. Honey collected by the bees and stored in their hives their source of nutrition. When you collect honey, you are stealing their nutrient source that is the result of their hard work.
 
When farmers collect honey, they replace it with a sucrose solution that is less nutritious than honey. To prevent the queen bee from leaving the colony, farmers clip her wings.
 
Honey is not collected by killing the bees but commercial farming of honey employs many cruel practices. Hence honey is not regarded as vegan food, as vegans avoid all products that are produced by employing practices that cause harm to animals in one or the other way. In addition to honey, beeswax is also regarded as a non-vegan product because the bees produce it to make their hives and commercial extraction of beeswax leaves the bees without shelter.