Why do you think so?

I dunno. Here is just one random stat that came to mind. Boston marathon participation throughout the years

  1897 - 18
  1930 - 218
  1970 - 1174
  2000 - 17813
  2019 - 30234

https://www.baa.org/races/boston-marathon/results/participat...

Still, would be interesting to see some comprehensive study on active leisure.

Meh. I would bet that has way more to do with the cost of travelling to Boston for the average person around the world and the growth in prestige of that particular event.

Also, athleisure is "active" in the literal sense, but is it contributing anything back to society? I guess one could argue it collectively reduces the cost of our growing passiveness. But I would argue, as someone who loves exercising, that exercise is just a video game that makes you feel progressively better the longer you play it instead of worse. It doesn't serve a broader purpose beyond a certain point of basic health, unless you are so good that other people derive satisfaction from your accomplishments (pro athlete) or you are doing it to form social connections (golf, intramural sports leagues, etc.) or like break a world record or something.