You can measure and modify the environment for a growing child/youth with relative ease; but you cannot modify genetic makeup at all (for now). This makes the distinction a valuable one.

Think of a car analogy: Genetics is the engine's size and type, environment is the fuel/tyres/lubricant that were added. Quite possible to get very bad performance out of a car with no engine oil or fuelled with diesel instead of petrol - but once these "hygiene factors" are addressed, the maximum performance is determined by innate factors.