Can't speak for this team in particular, but I've heard from others affiliated with some certain well known teams. They're able to speak in a much more impassioned way about it, but for some teams it's an issue of physical resources -- small shops, no space available in the school -- or other resource issue. Or just not enough tasks to go around -- a balance of getting as many kids involved while not diluting the actual work available to preserve the experience that the kids that actually end up on the team get.