Those other things aren’t activities people are currently doing. Bird watching is a social activity with clubs you can join right now.
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.
> A big part of birdwatching is identifying small, fast-moving animals that exhibit specific combinations of behaviors at specific times of the year based on specific climatic conditions. That sort of rapidfire pattern matching from video and audio info is probably a big contributor to what keeps the brain sharp.
It takes time and experience to build up your identification skills but it’s really rewarding and exciting and modern tech makes it easier than ever to learn