You can't just drill into the knee of kids to reconstruct an ACL, as you do with adults, because the kids' knees are still growing, and drilling into the growth plate damages the knee, as the article describes in one disturbing anecdote. There are some new surgical solutions for kids that don't damage the growth plate, but the long-term results are unknown.
As for adult ACL injury, the article says:
It is “the most common and most dreaded injury in professional sports,” Dr. Kocher said. The well-established operation to repair it often results in a full return to function. And doctors often recommend that adults have the operation because without the ligament the knee is not stable.