I have been a physician for 34 yrs, mostly as an orthopaedic surgeon. I have had the opportunity to treat many young athletes in that time. I have lost count of the times parents have been unable or unwilling to see the folly of their children participating in sports in the face of medical evidence that was overwhelming that it would be harmful to the child. Sometimes it's about money (usually in the form of scholarships on the line), sometimes the chance for a championship, notoriety, living vicariously through their children, and sometimes it is just the parents inability to comprehend the facts.
Sports are frequently seen as a way out of poverty, a way to get an education, a way to be important, or a way to justify the sacrifices of the parents. The kids almost always want to compete. That's what athletes do. It is my job to make sure they understand the risks and benefits. Adults can then weigh the odds and make their decisions, but in the case of children/young athletes, I feel obligated to err on the side of safety. It can be a very difficult decision since some opportunities will be lost forever. However, you only get one brain, one chance to remain healthy, and to sacrifice that chance can't be taken lightly.