Because they over-simplify the true picture. They fail to consider that all our biological status is an interaction between the phenotype and the physical environment. Lifestyle is a way of saying “different environments” and no more. However, it’s a useful phrase because when people talk about environmental factors, they usually refer to things external to the body, such as solar radiation, air pollution, smoking and so forth. Lifestyle incorporates these and includes other things found to be important, such as activity level, diet and behaviour, which are more “interactive” aspects between phenotype and environment.