Maybe there's some geographical or cultural differences, but I can say for sure that hobbies is a perfectly normal place to meet women in my area of the US. I have dated plenty of people I've met through hobbies.
Also I think there's a difference between picking up a woman at a gym vs picking them up at a running or biking meetup. I think just like with anything else, there are inappropriate ways to do it, but it's not socially unacceptable from my understanding whereas gym pickups really are.