I own a successful business and do software development on the side to supplement my income. I am not (generally) hurting for money. But you can bet your ass if the industry leader in my area of specialization offered unpaid internships that I'd be lining up to grab one.

If Mark Cuban offered an unpaid internship where the only compensation was to be able to ask him questions for 15 minutes per day, that would easily be worth forgoing pay.

So sorry, I'm not buying it. Perhaps the glut of college-educated individuals taking these "opportunities" are possibly at fault, no? Why is it entirely on the supply side of labor?

People and organizations at the top of their game can generally afford to pay. And may well want to, to avoid foregoing otherwise excellent candidates who outright need the money e.g. for immediate living expenses.