why is it better to promote physical fitness more than physical activity?

Answer 1

Well, physical activity includes a lot of different things. Someone may stroll in the park one time per week and claim that they are doing a physical activity, when in essence, they are not getting their heart rate up and are not doing anything to stay in shape.
Physcial fitness, on the other hand, (by definition) alludes to the fact that the participant is performing the exercise with the mindset that they are trying to become more physically fit - which is good for their health in the long run.