It's a matter of legality in the United States. "Among those criteria are that the internship should be similar to the training given in a vocational school or

It's a matter of legality in the United States. "Among those criteria are that the internship should be similar to the training given in a vocational school or academic institution, that the intern does not displace regular paid workers and that the employer 'derives no immediate advantage' from the intern’s activities [. . .]" https://www.nytimes.com/2010/04/03/business/03intern.html https://www.nytimes.com/2010/04/03/business/03intern.html