Not having to pay people is a great way to save costs.
Considering how valuable the benefit United received, United could have coughed up the money.
> In general, the more an internship program is structured around a classroom or academic experience as opposed to the employer’s actual operations, the more likely the internship will be viewed as an extension of the individual’s educational experience (this often occurs where a college or university exercises oversight over the internship program and provides educational credit).
It's still possibly over the line, and tacky as all get-out.
> The employer that provides the training derives no immediate advantage from the activities of the intern; and on occasion its operations may actually be impeded
This disqualifies nearly every unpaid internship in the country. This kind of thing is super common, and these guidelines are almost never enforced unless someone sues, but I just wanted to point out that this is not supposed to be unpaid whether or not the employer is feeling generous.