This is classic survivor and selection bias. You likely didn't notice all of the people sidelined by this.
I suspect selection bias also plays in to all of the negativity. But variety reigns and places that had more offerings almost certainly had more success.
EDIT: Since we've hit the reply nesting limit. I still don't see how having an activity that involves so many people sidelines anyone or how a lack of that activity would improve the involvement?
I can't think of any school sanctioned activities that discriminated against any student based on their appearance, even cheer. I had giant glasses that slid down my nose, a belly and braces. Believe me, the only thing that kept me from feeling included was my own perception of myself. Having coaches and a routine that forced me to exercise and lift weights was one of the best things I ever did.
How many ugly people do you remember that excelled at your school? Awkward people? Anyone that didn't have the support of being otherwise successful?
Edit: if you click the timestamp on a post, you can reply to it. :) Having an activity vacuum up all the money from any alternative sidelines folks. Did you have a thriving chess club? Go? Math or spelling bee?
I suspect selection bias also plays in to all of the negativity. But variety reigns and places that had more offerings almost certainly had more success.