Eh. I don't agree. My kids don't do any activities. They are 12 and 14. They don't want to. I could make them. It would probably "be good for them", but they are autistic and anything we have suggested has been met with a vehement NO. My oldest did adaptive Tae Kwon Do for almost two years until he got to the point he was crying through every class because he has such bad anxiety and was worried that he wasn't doing everything "the right way." Quitting that class was necessary, obviously. He has no desire to do anything social or team oriented where other kids are involved. My other son can't handle anyone bumping into him and has absolutely no stamina, so sports of most kinds are a hard no. Due to sensory issues, music of any kind is out as well.
I take them swimming every day in the summer. They swim laps, and one is probably good enough to be on a team, but he doesn't want to. Doesn't want the pressure to perform a certain way and prefers the solitude of swimming by himself. We also cycle together....long 10-15 mile rides on weekends on nearby bike trails. So they are active, just not outside of our family circle.
But I guess I already know my kids aren't getting into trouble. I mean, they are always home or at school. When (if) they are ready to join some activities, we will gladly sign them up, but I have stopped asking because I don't want them to get the message that something is wrong with NOT wanting to do activities. I do plan to have my kids get after school jobs when they are old enough. In my opinion, that's a far bigger life skill than anything a sport will impart. I played a ton of sports as a kid/teen: baseball, gymnastics, soccer, softball, swimming. I also worked in high school and value the work experience above all the sports experiences, to be honest.