We don't go birdwatching because we read somewhere that birdwatching is good for you.

We want to know what it is in birdwatching that registers as beneficial because if the factor(s) are distinct and isolated then the same benefits can be scaled outside of birdwatching.

And if you just went birdwatching because they said so, you wouldn't know why it might be beneficial to you. Or maybe there's a factor that wasn't identified separately and birdwatching itself doesn't improve your cognitive capabilities while, for many others, it supposedly does.

You would want to know you're getting benefits from whatever you decide to do if you're doing it in order to gain those benefits.