I think it really depends on the industry. If someone had offered me an unpaid internship for coding at any point in my life I would have told them no because I am aware that I could easily earn money or I'd probably be better off contributing to an open source project.

But consider the hypothetical in another industry. Someone gets a shot at an unpaid internship, they do really well, the company they are associated with gives them a recommendation, and immediately after the internship they get an offer for a position in that industry. Or: Someone does not get an internship, it is a competitive industry, the person ends up working an $8 / hr job for the next some odd years until they get an opening in the industry. It would seem the benefit to the unpaid intern could be greater than the benefit to the company.

Of course, there is the scenario where the person becomes an entrepreneur.