Because people are telling you they hurt themselves, they heard of other people hurting themselves, and they've found studies of people hurting themselves, and you're mystifyingly looking at them and going "no you didn't, you're wrong and I know your body and everyone else's body better than they do."

I LOVED cross country. I did it all through high school. And you know what? My hip flexors and ankles are fucking shot. The best runner on our team by LEAGUES ended up in a wheel chair for the end of one year because of shin splints. That shit absolutely will wreck your body, even if you like it, even if you're practicing and stretching daily, even if you're doing it under supervision. Some people will just have issues with certain parts of their body. It's not an attack on your passion that every body is different, with different limits and strengths. It is what it is.

It's great that you and others have been successful. We're all very happy that you've been able to it. Don't sit there and tell people they didn't experience the things they've experienced, that have had lifelong repercussions that they've needed to deal with. People are getting pissed at you because you sound like a pompous, dismissive jackass, dude.