That's no accident. A job is considered "unskilled" (or "unspecialized" as I like to call it) if any adult who's gone through the education system and is reasonably healthy can do. Since society would collapse without these jobs, we want to do everything we can to make sure we always have people who can do them. How do you make that happen? By designing the education system to teach everyone the skills to do them and making it mandatory to complete your schooling. As a result, nearly everyone is capable of doing some of the most important jobs for our society.