They don’t adjust for illegals who take up jobs previously filled by younger people.
When my son was in high school in the late 70’s he and his friends at one time or another worked in a gas station. Those jobs simply do not exist any more. So it’s not only the illegals that teenagers seeking part-time jobs must battle but laws which have been enacted as well as changes in technology. I do believe they could make a dent in the lawn care market but I can’t remember the last time I saw a teenager mow even their own lawn - at least not in my area.