Railersaileranyway, how did this come to be?
and why is it ony in action sports?
My guess is probably because it's a super easy way to advertise a brand. So sponsors give their athletes stickers and gear. A kid watching will see the stickers and think it's cool because their favorite rider is wearing it and want to do the same.
Action sports are different because when do you ever see a skier or rider wearing a jersey? To me a jersey is like sticker in action sports. It shows who you ride(play for) and you represent that company(team). If a kid has a favorite football player, they're gonna buy that players jersey. If a kid has a favorite rider, he's probably gonna buy from the brands they ride for.