Why is that a problem? The teen, not having to support themselves, has an advantage over the self-supporting individual, they can accept lower wages. In return

Why is that a problem? The teen, not having to support themselves, has an advantage over the self-supporting individual, they can accept lower wages. In return the company has a choice, to employ teenagers for less money and dealing with the consequences that they are part time or seasonal, or to employ the individual that demands a living wage for themselves and dealing with the consequences that they are full-time and rather permanent.