From everything I've read (been a while now), but I'm under the impression that kids arms are overused before they are fully developed. It starts back in high school where the demand and play time is extreme, they play all year round now where years ago it was just a handful of games beyond their regular league. It's no surprise that most Tommy john injuries are to younger pitchers, development has changed a lot over the last 20+ years for better and for worse. If you consider the amount of camps, tournaments, etc. that get organized from since having access to the internet alone is big. I think it all compiled in to a bigger problem that perhaps no one has really grasped the extent of it yet.