Because the benefits that can be seen through continuous exercise and fitness take a long time to be obtained. Few people are willing to spend so long or so much effort on something like this. So no one is willing to put their money here.
In fact, the process of everyone investing money is actually called investment. You can invest in others, and you can invest in yourself. So many people are willing to spend their money.
But the premise must be that you feel that this thing has direct benefits. If you can see the benefits come out quickly, this is a better thing.
On the other hand, continuous exercise or fitness is completely inconsistent with this concept. The first thing you invest is yourself, the effect is not very obvious, and you need to have strong self-discipline or self-control.
And you are not sure that you will have a very good result or a very good income, so most people are not willing to make this kind of investment because they need to pay too much. And not sure there is a good outcome. This is why so few people are willing to spend money on this kind of continuous exercise and fitness.